[Lvl 1] Simulators... mostly

Breaking this into two parts, tl;dr at the bottom:
(This post is somewhat of a tangent, skip down to the second post below if you're not into deliberations about language.)

Simulation:

Simulation is a genre where a simulated environment is created to answer any "what if" or "what would it be like to" question. That simulation in no way has to attempt to be realistic, though many subgenres do put a preference on realism, and most Simulation games at least attempt to incorporate some real-world foundations. Nevertheless, "What if humans could fly? Let's simulate a world where that is possible" is very much an exemplification of the genre, as much as "What would it be like to drive a semi-truck through Europe?" or "What if I was a god-like being in control of a civilization?".

Euro Truck/etc would fall under Vehicle Simulation games (and possibly also Driving Simulation, if such a game has an emphasis on realistic controls in conjunction with the appropriate hardware). Any game where you control and develop at least one artificial lifeform or otherwise manage an ecosystem would be a Life Simulation game, a major [and very broad] genre which has the notable "God Game" and "Genetic Simulation" subgenres beneath it, along with encompassing games like The Sims.

Arcade Game Simulation [such as digital Pinball games], City/Civilization Building Simulation, Combat Simulation [sometimes further subdivided into Soldier Simulation and Warfare Simulation], Dating Simulation, Driving Simulation, Farming Simulation, Flight Simulation, Life Simulation, Management Simulation, Medical Simulation, Photography Simulation, Social Simulation, Sports Simulation, Survival Simulation, Tabletop Simulation, Train Simulation, Vehicle Simulation.. Those are just the subgenres I could think of offhand.
Moreover, the entire "Racing" genre is, I believe, technically considered a subgenre of "Simulation".

Flight Simulation is a good example of realism vs fantastical- the genre covers the experience of flying realistic planes (and Flight Simulators are famous for their emphasis on realism) but also can cover the simulated flying of spaceships.

"Work Sims" was a meta-classification I was familiar wth in the past (though I'm not sure if it's still in use) for games which attempted to as closely as possible mimick even the most monotonous elements of the real world [making them feel more like "work" than "play"]. Generally, that term was associated with "Realistic" simulation games, most specifically the ones involving completion of productive workforce tasks.

In a sense, realistic simulators are to the simulation genre what HOGs are to the point n' click genre [which has the primary subgenres of PnC Adventure Games, PnC Puzzle Games, HOGs, and Myst-Likes]. The most visible games within the overall genre are likely not going to be from that subgenre, but the subgenre has a dedicated fandom, an overwhelming amount of releases, and wide-spread visibility that makes the subgenre itself stand out more than the other associated subgenres, despite the most high profile games typically coming from those other subgenres.

..of course, that comparison has one major flaw, and that's the fact that I don't believe anyone has ever spent thousands of dollars on any single HOG game before. (I mean, wow, that'd raise an eyebrow.) The same is almost certainly not true for some of those realistic simulation games, such as Train Simulator (which is currently showing me $9,131.72 in DLC).

Anyway, in summary, "Simulation" is as broad and inherently vague as "Action" or "Adventure". You don't entirely know what that's going to mean until you look at the rest of the genre description. Given how realism can be found in most any of the many Simulation subgenres, a "Realistic Simulation" subgenre label seems to never gained any real traction. Instead, it appears to have become standard to simply add a "Realistic" tag in with the game's existing Simulation tags, for easy combined tag referencing.

I'll likely never understand the appeal of "work sims", myself, but Simulation is a label that's broad enough in what it covers that it can really find something to appeal to most anyone. :)

..and also is broad enough that it doesn't really tell you much when it's used as a label for a sale promotion. ;P

Simulator:

One meaningful quirk of language I've noticed is that "Simulator" is generally applied to realistic Simulation programs, while "Simulation" is typically applied to non-realistic ones. (In fact, when I google "Simulator", definitions for the term specifically state that it refers to realistic Simulation programs exclusively.) Simulator is also a term associated more with developing a skill, rather than with gaming [while Simulation is mostly associated with research programs and games].

However, I've also seen the two terms used interchangably a fair bit (though, going off established usage, it seems possible that they shouldn't be, much as how co-op and team pvp shouldn't be, yet often are; On the other hand, one could argue off the inherent word structure that a simulator would be any element which presents a simulation, and thus that the two terms are in fact somewhat inherently interchangable), which is likely the cause for why Humble named their promotion as they did. That said, I'd agree that "Simulation" would have been a better choice for their bundle, as that is the actual genre, rather than being a related term with a strongly-established, slightly different implication of meaning.

It also wouldn't remotely be the only time Humble has poorly considered the title of a promotion. At least this time they weren't accidentally(?) cheering on the concept of war orphans, like that one time..

On the other hand, given that game titles themselves seem to make so little distinction between the two terms, it can be a bit hard to judge Humble poorly on this particular incident.

tl;dr version:

The issue is a difference in the expected meaning of Simulation and Simulator, and your interpretation is entirely reasonable given that Humble chose to use Simulator rather than Simulation.

That long technical deliberation aside, I'm pretty sure there are games in that list which aren't valid for either the simulation or simulator label- like, Sakura games? Nothing dynamic is occuring to emulate specific environmental conditions and their effects, nor are you able to affect simulated environments through catalyst actions, nor are you able to place yourself within simulated environments to experience situations through your own perspective. Dungeons and Omerta seem like rather a stretch, as well. :P

Maybe they didn't actually mean Stimulating Simulators, but Stimulating Games + Simulator Games? :P