I agree - one of those awful Oops's! They happen, not only to caregiver's but to parents; it's tough. We are held to a higher standard (as we should be) and when we fall, it is a much, much farther drop.
I agree with your husband & mo4, let it go and learn from it. Next time a drop-off like that happens, hold little Johnny's hand until mom has gone and he won't surprise all of the adults by running towards her car.
How was she at pick-up?