The incident in combination with the "shouldn't have provoked the poor guy" phrasing from event staff makes me think ASD, not that that would justify anything obviously, but it kind of explains why they might have let him stay at first. I had to take annual crisis prevention/intervention classes when I worked as a direct support professional in group homes and biting is a whole section of the training.
If someone (or something, works with animals too) is latched on, the first thing to try is to push whatever's being bitten into the bite. This fills the mouth which can trigger the release reflex, or even the gag reflex, causing the mouth to open. The other main technique for human biters (idk if it works for animals, probably species-dependent), is to put your thumb or finger under the base of their nose and apply pressure upwards, or rub back and forth. It's hard to trigger on yourself, but if someone else does it to you, it apparently really hurts and also triggers the release reflex. The biggest things to remember are not to pull away and not to let them pull away.
Thankfully I've never needed to use these techniques, I mostly dealt with verbal and other non-physical behaviors.
