I could be wrong but I don’t think Gaijin was created or contracted by the military to make the game.

I dunno, in effect it's military propaganda. I know the game America's Army was funded and promoted by the US army at the time.

I think it's the other way around : due to past propaganda, Russians really like tanks. As a result, tank games come from Russia.

I think there is probably a genuine desire for people to play a realistic game w here you're in large, heavily armoured weapons of war. The game in question has tanks from almost every nation that has ever produced tanks, so I'd wager it's either a consequence of propaganda rather than propaganda for military per se.