People are very different in the way they handle constructive criticism. Some people are far more equipped to handle it than others. We think out of all the professions, though, the people who should be the most adept at it are teachers. After all, they dish it out the most!
Apparently, not all teachers have the same mentality. What makes it even better is that it comes from the student that the teacher respects the most. Something tells us this guy had a deep, long talk with himself about his teaching methods that night. Hopefully, he has changed his habits.