If he is talking about having children with her, he obviously doesn't know. Unless they are planning adoption.
If it was me, I would want to know. Maybe he has no idea. Or maybe he doesn't care, but if he is 100% heterosexual, he probably wouldn't like being led up the garden path by this partner. And that is the problem here, the possible deception if she hasn't told him.
I knew a guy that was seeing a ladyboy here while on holiday, and had no idea. Once he returned home, he invited her to go visit him in his country, and asked for a copy of her passport to aid getting her there.
Once he received said copy he said "There must be some mistake, this is a man's passport. I need your one." This led to some shock on his part when the light finally went on in his head. Needless to say, communication went dead from his end after that.