He understands genetics and these days, when talking to the likes of Piers Morgan et al. he plays a cagey game and talks about reproductive sex, what is required to make a baby outside of a lab the good old fashioned way, when a sperm fertilises an egg.
He's well aware there are more than two types of human birth, he glosses over what he knows to keep things simple to avoid contraversy or something.
If this is all news to you, rather than something you might have read, as I did, some 40+ years ago, then you might choose to start with:
https://en.wikipedia.org/wiki/Intersex
IIRC it links to medical papers and meta papers.
There are several people here in Australia that were born neither male nor female. That's a fact. One took a valid complaint through the Australian courts that they would be lying on an official document if they checked either [F] or [M] on an Australian passport.
Doctors and genetics experts gave evidence, the Australian passport system was changed.
This wasn't some "cultural gender" thing based on someone's feelings about gender, it was stone cold genetic reality about "sex" at birth .. which in reality is a lot more complicated than many Fox cable hosts claim it to be on camera.