I agree. He would have had a code.We all know that God would have had Ishmael stoned for such an offense just because the law ie Ten Commandments doesn’t mean Abraham didn’t have some kind of moral code
I’m not even saying I believe the theory.
But, I don’t think they postulate that Ishmael violated his body. I think they feel it was sexually inappropriate.
Regardless, I think the bigger picture is that folks will grasp at straws to shoehorn in a biblical reason for Jew/Arab discord.