I understand that somebody may not want to raise such a matter personally.

The real problem is that OP wasn't even given the details of the accusation. Because even assuming that the accusations are correct, there is likely no malice involved here (not by OP, taking his word on this, and probably also not by the other person, given that he's in an internship). Without the details, OP has no opportunity to correct his behavior and might make the same mistake in the future, whatever it was. That way, everybody loses.