I think I would have been perturbed with the parent who felt the need to proclaim eel loudly. I suspect that parent went home and looked it up only to find that they were in the wrong. But I do understand your concern about 'know-it-all' attitude and the knocks he will get along the way. Today might be a good experience for you to discuss with him. That it isn't necessarily the facts but how we present it that can change the outcome. Perhaps he could have listened to the arguments of the other kids and found something positive to respond to without giving in to them?