Am I rude for calling a cross dresser sir?

I live in Philippines and I work at hospital as an admin assitant and the woman asked me for medcert and I assisted her and she's with the dude who wearing a spaghetti dress and she gave me a hospital bill I said "Sir its for cashier" and he replied " Well go there after we go to Care building (the discount building for medical bills) and my coworkers corrected me I should have called her maam because he's a crossdresser and another of my coworker said its to respect them. I just remain silent but in my mind its a dude like why would I call him Maam instead of Sir? Am I rude? Like wth
Am I rude for calling a cross dresser sir?
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