Alex has had that response before. It's okay!

"No. The Federation is made up of at least two or three dozen different races. Humans seem to be most of Starfleet, but we are not all of it, by far." He grinned at her. "May I ask, and tell me no, if it offends somehow, but what race are you?" He knew the legends of centaurs, but she seemed nice, so he was predisposed to discount them.