If you read this letter I encourage you to read the Chomsky interviews they linked. These interviews were my first experience reading things he wrote or said. After reading those it seems like the authors of this letter didn't really understand his statements.

I don't agree with everything Chomsky said, but he seems to try and understand all of the opposing viewpoints in this conflict as a way to figure out what the possible outcomes are. It didn't come across as blatantly or negligently pro-Russian to me.

For example, I think its pretty reasonable to hold the opinion that Ukraine probably isn't getting Crimea back without forcibly taking it (and I have no idea if they are capable of it). Chomsky and I could be wrong about this but I don't think it makes either of us pro-Russian shills. He's not attempting to predict what ought to happen in the fantasy world that we want to exist, he's trying to predict what may happen in the deeply flawed world that we actually have.