No, that is not even remotely close to qualifying for any of those things.

The principal merely said someone made a call about it, they didn't present that claim as a fact, they didn't publish it, they didn't act with malice or negligence, and they caused no damages. A statement would have to meet all of those qualifications to be libel or defamation. It meets none.

Harassment is repeated or continuing communication that serves no purpose other than bothering the person. This was a single phone call was made for the purpose of investigating an alleged school incident. It meets none of the qualifications to be harassment.

Our laws do not prevent anyone from discussing claims by other people that may or may not be true. It would be silly if they did.

There is absolutely nothing illegal nor unusual for school staff to call parents to investigate concerning claims made by other students or parents. Doing so is exactly how misunderstandings in these situations are cleared up.