i think it would be best to have a discussion with the teacher. get the whole story and her side also. she may not have realised how much food you packed or he consumed.

i would be upset also as i feel she stepped over a boundary. why give your child money? how could she "feel" he was hungry, did she ask him?

definately have a talk to her openly about it but let her know that it did not please you to hear what had happened.