Actually, since he was in a occupation that deals with all kinds of people, he should have been aware that a person in a dress, would rather be referred to as a lady, not a gentleman.
Even if that is not so in all cases, I would say it was so in most cases.
Next time, take the person aside and quietly ask that they refer to you as a lady when you are in a dress. Then there won't/shouldn't be a next time with this person for you or the next trans individual he comes across.
