If they are doing so because of a shitty employer, drawing attention to their real or perceived gender nonconformity could make things worse for them. You could also just be wrong and actually looking at a man that seems feminine to you; it’s very common for trans men to be assumed to be trans women if we’re not passing as men.

I recognize this is absolutely coming from a place of compassion and empathy, but the best thing to do with a stranger is take them at their word and be courteous. There are a ton of things that could be going on when someone introduces themself with a name that seems to contradict their gender presentation, and trans woman forced into it is only one of many possibilities.

A trans person is even more aware of how shitty a situation that is, which means, when they tell you their name, they're aware of the consequences and are telling you what feels appropriate for them. The best thing you can do is trust them, and follow their lead.