So, your only yardstick of whether it was right to do is if something dies as a direct consequence? Hmmm. Guess you're okay with chum-the-water shark dives, fish feeding, collecting "dead" coral and shells, etc etc. I mean, nothing dies as a direct consequence of one feeding, chumming, and the like. Longer term behavioral changes or acruing damages are just someone else's problem?
I understand this was probably a 'once in a lifetime' type event to happen to those present, and judgement can fall by the wayside when excitement reigns. I wouldn't have tried to speargun anyone for grabbing hold. But I don't like seeing it, and hope to he** if ever put in that position myself I would act differently.
I also understand no diving is truly "zero impact" - dive boat to get you there runs diesel or gas engines, emits noise; lights used at night can inadverdantly flush prey out and spotlight it for predators; even bubbles flowing along a coral wall can do some damage regardless of whether a diver is cautious to watch trim and buoyancy to not make bodily contact. Guess you and I just draw the line about what impacts we can (and should) prevent a bit differently.