@Albadross
It’s a really tricky one. I’m not sure there is a right answer. You being autistic is something that would concern me, because I don’t have a complete handle on how that might impact on this discussion with him, should you choose to have it.
Although, as a pp said, you seem to be managing boundaries pretty well. If this thread is anything to go by.
It’s very tempting to want to speak to him, I can see. He also doesn’t sound like a crazy transactivist. Is he a late transitioner? Has he been married? Is he gay?
Whilst not foolproof, if you knew the answers to those questions, you might be in a better position to know whether he was a straightforward gay transsexual, or an autogynephile. If he is the latter (not gay, late transition, possibly been married), then I would stay far away.
If he is the former, then it’s more difficult.
Either way, as someone else said, the risk/reward aspect of this doesn’t seem worth it.
Tempting though it might be personally, your actual gain will be relatively small.
Are you worried about putting him off now?