His name would not be used in the announcement, if he was not a member of the staff at the school.

It could have been. (By the way, I made that theory up in one minute - it wasn't meant to be foolproof.)

It is unlikely, but if he would have ties with the school to the extent that everybody in the community knows who he is, then maybe. But how would he know the students stayed after school? It would be a much better idea to wait until school hours, to ensure that everybody he saw at the store was at school.

It is a good theory for one minute.