The straw they are clutching at is that being male and effeminate has been considered unacceptable in many cultures through the ages, and so in societies where male and female roles were particularly strict, there were often communities of (often gay) men who dressed in clothes that were generally considered more feminine than masculine.
In addition, when women had few rights and as few opportunities, a few women would dress in men’s clothes and pretend to be men in order to do things that women couldn’t.
These fairly well documented facts are somehow proof that there were always “trans people” and presumably between them, they represent all 72 genders.