I don't know why you brought that up. I'm sure he stopped to help at the scene because he thought he could help, and not because of some interpretation of an "oath".
Doctors in the US are not legally obligated to jump in when a person is having a medical emergency. In fact, we've seen cases where they have and then faced lawsuits.

The AMA does expect doctors to help in such situations, but it is a code of conduct and not a legal issue.

Besides, even if his oath said he had to do it, the person benefitting from his actions would still owe (at least) a huge debt of gratitude. Just because you are outside of a typical clinical situation doesn't mean you are deserving of free medical care.