Riker knows where Data's off switch is as well as how fully functional he is.

To be fair, the whole plot point is that their species appears androgynous, but they aren’t always. The one he falls for is explicitly female, which he noticed subconsciously, and comments on once she reveals that she is actually female.

So I’d say he so much into women he sniffed out the estrogen in a species that tries their hardest to appear genderless. The ultimate heterosexual.