I think people have the wrong idea
from the comment's here it appears people think the 'Mutants are people who where exposed to Radiation , become violent , escaped the authorities.'
If you look closely the people are obviously mutant's, than have become this way over the last 25-30 year's, producing deformed offspring , some without or shortened limb's.
The idea i guess is these are some of the original worker's , inhabitant's or soldier's from the 80's who as it was still the USSR at that time where held in captivity.