Even with bad experiences people may have had with EWR agents, this seems unbelievable. Either the agents needs to be fired, or his version is exaggerated; I'd lean towards the second, though that doesn't excuse poor people skills.
But this goes along just like the Carry-on Gestapo thread. Rules are rules, and every time they're not enforced, be thankful that you managed to slide by. But never expect that to happen, and always be prepared to make alternative arrangements. I agree, and am in shock, that someone of this caliber (olympic athlete) would wait until the airport with his stuff, and not make sure that if his items weren't allowed on (which he admits he knew was the rule) there were alternative arrangements in place.
I find his retort, “You are merging with United. United is an Olympic partner. I chose this airline for a reason" to be a bit weird. If that's the case, shouldn't UA be flying him (as opposed to him booking on his own)? Otherwise, since this isn't the Olympics, and he's booking in his own, why should any airline care. (Although, the FA's response is weird, as it doesn't matter what's written as they're one company now.)