It sounds like the teacher overreacted but if your son was mimicking him he was being disrespectful. I hope you acknowledged his ill behavior and handled it so he doesn't continue to be disrespectful in school.
Wow -- thanks captain obvious! Seems like you get some kind of high from reading posts, assuming the worst about people, figuring that nobody except for you knows how kids ought to act, and what constitutes acceptable behavior, and then schooling them on proper parenting in an obnoxious smarty-pants fashion.