The latest research in genetics show that there is no connection between heredity and brain capability.
The reason of the fact that you've mentioned hides in educational system. In USSR schools children were taught almost every single aspect of those times science without testing childs predisposition. This could cause major psychological deviations, which were not counted at that time.
So yes, erudition and general knowledge of people from former Soviet Union can be higher, but there is nothing related to heredity.
Jews were considered and still are considered good with their brains.
Russians are too considered good with their brain, many successful american companies being the mastermind of Russian immigrants.
Now we're talking about Indian and Chinese scientist.
Does heredity have an effect on the brain?