chernobyl happened almost 40 years ago. there were a couple of generations in russia ever since. chernobyl wasn't even in russia. why would random russian rural dudes (majority of army. people from major cities are rare) will know that it happened ?

The mistake you're making is projecting your personal experience onto others, and extrapolating your personal account to everyone.

In the meantime, the Soviet union employed a massive censorship and disinformation effort regarding the Chernobyl accident, and Russia's invasion force deployed throughout Ukraine is renowned to originate primarily from remote regions of the Russian federation.

Just because you have access to the internet and CNN and benefitted from living in a society where information flows freely, that does not mean that random people from Buryatia enjoyed the same privileges.