My guess is if he was hooked up with a social circle there and is good-looking (it seems like he probably is), then yeah, it's believable. Russian women are insanely hot. You'll see 4-5 girls every day there that you'd go weeks between seeing in the US. They also respond very well to aggression. So yeah... I could see it. He may be exaggerating a bit. But it's not totally unrealistic.

You gotta realize though, him having a social circle waiting for him was huge. Game in Russia is all about self-selecting the English-speakers and girls who are interested in Western guys. This is hard and can take a long time because like 10% of the population speaks English. But if he landed and already had a group of girls who were interested in Western guys lined up, then yeah, massive opportunity. And if you're good-looking and have game on top of that. Yeah, you'd kill it there.