Sounds like some kind of an irrational panic on his part.

I'm a cis gay man who has never felt an ounce of attraction to women. My body and mind just don't work like that. I have sometimes felt strong attraction to trans men I've met or encountered on line. That in no way makes me not gay.

I've never had occasion to date a trans man, but if I ever did, I'd still be gay ... obviously.

Some people need to chill.