TBH, if you are a top scientist, or whatever, and you meet a rich admirer who wants to donate some $$$, it is very easy to accept. Chomsky probably knew this was just a way to give $$$ to him, but he didn't see anything wrong with it.

Why do you find it implausible that he got money to develop this challenge? I work in the non profit space and we get these kind of gifts all the time, with minimal strings attached or sometimes the deliverables don't see the light of day. 20k is actually small in my experience and they often come from random people who support our mission. Sure we do investigate and sometimes refuse based on findings, but we don't know or find everything. Taking money doesn't mean you know and support everything the person who have the money ever did, thought, said...

Noam strikes me as someone deeply attached to their "art", honestly this "linguistic challenge" feels like a nerd-snipe and Noam might have even done it for free.

I think the payment aspect works more in favor of Epstein than Noam. I don't think Epstein was oblivious to the "we go down together" nature of some of his relationships, quite the opposite.