Regardless, it's a hobby that he really enjoys. I agree that he doesn't see it as sexual at all, but there's still no need to shame him about it. But on the flip side, there's no need for him to shame her about not liking it. I didn't like that my ex boyfriend skydives, but we both just accepted that neither of us was going to change the other's minds.

If she doesn't like this behavior (that has existed longer than their relationship and is honestly harmless, even if a little strange), then it is up to her to either learn to accept it or leave. She shouldn't expect him to give up his hobby for her.