[FREE] Life is Strange - Episode 1...till 15.01.2018.

sale ends 15.01, ep 1 remain free

I'm sure the time tag refers to the ongoing sale (which is the complete bundle of episodes -75% at 5€).

Nah, it's free forever, but the whole series is on sale these days so it looks like that.

As I understand

For that, you can blame Valve for their continual refusal to update elements of their service to function more coherently.

Any time something goes on sale, it uses the top-level (ie, most heavily discounted) item on that listing's store page.
(This is tied to the same reason individual daedalic games pick up the CV of daedalic packages during sales.)
It also typically attempts to reference the title of that store page, rather than of the specific item on sale.

What that image says- and you can tell by the 75% off at the bottom- is that there's currently a 75% off sale on [the associated store page for Life is Strange Episode 1], a page which has the title [Life is Strange Episode 1] rather than [Life is Strange] (So you can actually blame the publisher a bit for that as well). The sale prompt then takes the top level listing, assuming that's what's being referenced, and notes its price- which happens to be free.

Basically, it's just a hot mess of presentation, but it actually doesn't have anything to do with Episode 1 at all.