Oops. Hit send instead of return. I had more to my point.
I can see your point that you wouldn't let him walk home alone. I can't really disagree.
However, there is also a question of an appropriate reaction once it happened.
Here, the mother might be justified to complain to the school, but instead she is parading her child around and acting in a manner that, basically, tells the child "oooh, you poor little thing, your almost died, make sure you stay upset."
She sent a message to the child to whine. She should have been brave in front of her kid and, if need be, ripped the teacher a new one in private.
Well, if she ripped the teacher a new one in public it might accomplish more. I care less about how the mother acted than how that child was treated by the school.