If the student's course sampling story is genuine, then this professor has accomplished nothing more than being a jerk to an engaged student. There is no reason

If the student's course sampling story is genuine, then this professor has accomplished nothing more than being a jerk to an engaged student. There is no reason to interpret 1 hour tardiness of a single student as disrespect. Consistent 10 minute tardiness of a large portion of a class or a single disengaged student? Now that's a different story. The only time students entering or exiting make much of a distraction is when the instructor calls them out on it. However, it is more likely that the student's story is bullshit. In which case he or she shouldn't have bothered to send that email. Both people are at fault here. The student shouldn't have written an email when a simple "I'm sorry, bye." had already resolved the issue. The professor should have assumed good intentions and kept his unsolicited advice to himself. Especially if he was going to be that rude about it. He could have simply ignored the email. That is what my political experiences have proven the safest course of action to be.