I am not because I am Russian :) Seriously though, this joke is an example of a classical sub-genre of Russian jokes where Russians prove their superiority in various areas of life (including, ironically, heavy drinking) over westerners (usually Americans, but sometimes French and Germans).

Any unrealistic assumptions are irrelevant, punchline is all that matters :)

I've heard the joke before in various forms, most commonly using two prestigious British public schools (Harrow and Eton). I wonder what the original form was?

The joke is hilarious, don't get me wrong, I just found the assumption kind of silly too :p