I’m also rescue trained and couldn’t imagine doing something like that. I wonder if he turned her air off when she wasn’t looking. Probably pulled her regulater out of her mouth.
Isn’t there a rule about the regulator? Like if its found in their mouth then they ran out of air. If they’ve spit it out then theres something else that went wrong.
Not 100% reliable but it was something told to me by my instructors.