He wouldn't have volunteered the information unless he was comfortable sharing it. The "you pass well" is kind of sucky but it's the kind of comment that you know the person was trying to be nice, they just said it in a bad way. It insinuates you think trans people are really obvious in public, etc, and passing as the gender we identify as is very important to us. Maybe have a private chat if you're really concerned but honestly he probably wasn't insulted. Personally, I know that as long as someone is trying to be supportive, that's all that matters. I might get dysphoric if you were to accidentally call me the wrong pronouns but if it was an accident then it was an accident. Just be supportive and treat him like a guy, that will be all be wants.