if i take my horse to a clinic and get dumped, it's not the fault of the trainer. there is some risk involved in riding. if i take my horse to a clinic and the trainer throws a firecracker under her and i get dumped, that is the fault of the trainer. she/he used poor judgment.
if i am smart, i wear my helmet to the clinic, but if i get dumped and break my arm, the helmet did not help.
i don't think the organizer should apologize either. i do think he should have a word with the presenter and not have that person back again. in many of our activities there is a risk that we assume. part of that risk should not be accepting injury because someone else demonstrated poor/no judgment.