My Dh did this years ago on a date and when asked why he was so certain that the date was incorrect he told the lecturer it was his wedding day. Lecturer had to agree he knew what he was talking about. It was done in a nice way and he never had problems with the lecturer.

As he is in a place of teaching he should be informed that his wording is incorrect and I would do this before the subject is finished so he can inform the class.
No person is always correct. being corrected is how we learn, it's how we correct that is the main issue.