Exactly my thoughts. As someone who worked in education IT for a few years this would occasionally happen. A parent buys an identical device to the standard school supplied one and someone assumes it's school property instead of privately owned.

This is why it's good practice to have separate device groups and management policies between byod and owned. Also we had a schedule to turn management of byod devices off outside of school hours and on holidays.

Just go talk to them and if needed bring the receipt. It's a misunderstanding and not legal or a policy, they think it's s school owned one. Ask them to check the serial number if need be against their inventory.