Not true, there are/were North Korean hackers actively using platforms like Hackerone and other lesser known SaaS that haven't implemented KYC for training.
I think this was a pretty stupid joke. Especially if the OP is an individual. Making a nation state your adversary as merely a sole individual is something you never ever want to even risk. Any rational human being (not just hacker) would know or recognize that. Very often it is ego that directly leads to doing irrational actions like this.
