I can't see someone putting down an authority to pickup a child, when the person lives a good distance away to pick-up the child from school (at a moments notice with a tummy ache or injury). Doesn't seem practical especially since Mom was a stay-at-home Mom. It could explain an a unique / isolated incidence if that were the case, and if he were on the form & it counted as "legal" custody so as not to count as an abduction, I would agree.
I know on our releases at school, we have 2 different authorizations.
1. To call in an emergency-locals only.
2. Authorized to pick up. They can be from the moon if the parents wish.
The emergency contact has to be authorized to pick up as well.
I find it IMPOSSIBLE to believe with the uncle looking at those charges ,that he would be on the family's authorized to pick-up list.