Well, since it is the rule, I think it was enforced correctly. He could have made that pass w/o going so low, but he chose not too. It looked especially bad because he was moving down at the same time the other cars were moving up, so no way to say he was forced down.
I think not having the rule would just invite more accidents, something everyone criticizes already. Was a great attempt, and I'm sure he'll have plenty more chances.