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.