I can't believe I'm delving into this, but...

He/she suggests one or the other, not both genders at the same time, and in that case I'd say Jinx is right. It's like an unknown or a flickering between the two options. If it were he-she, then that would suggest it is a combination of some kind, which would probably take it outside the binary.

I'm going more by grammar rules here than a massive education on gender though