Not sure if being rude, or misunderstanding. Perhaps they just have set rules, and didn't want to be rude, but still had to tell you. But that does seem like a dumb rule. But you know, if you want, you can make your own homemade wax, and just use strips of a cut up old shirt, and it works just fine. Here's how to do it.
Otherwise if you're still persistent on this appointment, I guess it can't hurt to at least say that you are trans. You wouldn't know unless you try if that would make a difference.