I think it's highly contradictory, but when it comes to self applied identities like gender or sexuality I firmly believe it's only the business of the person who is identifying. It's not a definition thing to me, it's a self determination thing.

He's probably either in the closet or hasn't unpacked the ways he equates masculinity with penetration enough to open himself up to his femdom desires.

Either way, he's still allowed to call himself straight, even if he's pretty clearly mistaken.