This actually makes perfect sense after reading "Immigration and Cultures" by Thomas Sowell.

He specifically cited that migrant populations will tend to take not only their knowledge, culture, and traditions from that specific place and time that they left with them.

In essence, all that makes up human capital are actually pulled with the migrants.

He also noted that systemic and institutional discrimination against these immigrant groups does not necessarily change or diminish their human capital.

Now, I think both he and I agree that there would be some limit to that, as human potential can be degraded through enough systematic abuse. But the point still stands that some abuse is not simply enough to diminish human capital, which each individual may find is one of their most important features for overcoming such abuse.

If we were then to selectively intentionally relocate high-human-capital individuals and condense them into a concentration camp, and even expose them to abuse, the human capital they took with them into the concentration camp still remained.

That's probably what happened here. They used their human capital (in the form of ingenuity, discipline, and long term time preference) to survive the gulags and maintain sanity, then managed to leave the gulags and recover from the ordeal while keeping their wits about them the whole way.

This is also proof that as devastating as communism is, it can't necessarily be destroy the foundations of civilization without total genocide.