Well he did post a one-liner when they were looking for Dorian Nakamoto
I'm confident that was fake. If Satoshi really wanted to prove that it was himself making that post to that other forum, he would have signed the post with his private key. He is very aware of the need to prove who he is and how to do so.
and I think at some other instance as well.
I'm not aware of any other public instance. If he's alive, it's possible that he might have continued communicating with Gavin, Theymos, and others privately.
He is on the forums for 100% but just hidden under another name .
Theymos know him for 200% also , I don't think see how he would try random guy on the internet to lead one of the biggest forums on the world if he don't know him In real life & don't trust him .