why?

Statistically it's a big warning flag, so it's honestly not unreasonable to include that. I'd bet a higher proportion of Russian users on this site have made fake giveaways than users with VAC bans for example.

As to why this is a problem in particular I have no idea; maybe it's just a really poor grasp of English?

I wrote explanation below. There is rather solid reason to put Russian or Ukrainian into a cons list for DayZ gift.

depends

Misunderstanding creating a giveaway is often due to translations. Still, the whole list is sort of insulting, if someone thinks it's fake then they should just move on or at most use that report button.

As you know there is a value of account here on SteamGifts which allows to participate in some limited giveaways of good games. So, when you giving away a game you usually want to boost this value by giving away pricey games bought on sale unless you are shamelessly rich and just want to make someone happy for no particular reason.

How is it connected with Russians? Majority of games on Russian store is 1/2 price of USA store (and price in points here) and that is for a reason. Majority of Russian people just wouldn't buy a game for a $50. It's just too much for them. So, even AAA titles are usually worth $25. WATCH_DOGS Deluxe for $32 instead of $70? Sure. Actually Uplay key of it is available for ~$17 right now. Same goes for Ukraine and some other countries around Russia too but Russian prices are usually the besst.

Of course part of such games is not regions free. So, it's not possible to gift something like Skyrim here but if I'd aim to boost value of my account (and that's something most of users here want to do first) I'd think about something like Counter-Strike: Global Offensive (especially if it were bought during the winter sale) or L.A. Noire (it worth ~$10 while gives 20p due to $20 price in the USA store and were on -75% sale just 2 days ago). Or if I'd like to be a "villain" I'd try to give away something region-locked in the small steam group of people which I can warn about giving-away region-locked version of the game to avoid gifting it to someone who wouldn't be able to activate it.

DayZ is different. It worth $30 everywhere. Well, it's not the only game which haven't regional price for Russia. I just want to say that there are more interesting alternatives to boost account's value. This one were on sale only twice and only for 15%.

So, it's rather unlikely for someone from Russia or Ukraine to buy it as a gift to give it away here on SteamGifts and this guy gives away 2 at once! It could possibly be true but probability is rather low.

Why someone may want to create fake DayZ giveaway in the first place? Probably because it's first region-free game in the aggregated wishlist here on SG. A tlast I see no other reason for that. At least a new user who have no idea how SG works but already noticed limitation by account value may think it's a good idea to pretend giving away something everyone wants to have here.

BTW, judging by his favorite games (Dota 2 and GTA: San Andreas) and his nicknames I can deduce that in the best case scenario he is a student and in the worst case he haven't even left school yet. So, chance for him to be just rich and generous is even lower.