So interesting. If they already got the scores back I would have to assume the tests were not flagged. And if they were, like you said, the school chose not to pursue. But wouldn't the test itself (rather than the school) be the one to choose wether or not the tests should be flagged and subsequently thrown out? It is a really rare situation.
I caught someone looking at my paper once in middle school and told my best friend. She stated she saw the same person looking at her paper during the same test. We went together to the teacher but I am not even sure the teacher believed us or acted on it as the student was typically top of the class. We both thought it strange too.