Sounds like the teacher is insecure. In your place, I wouldn't endorse an apology. Your son was matter-of-fact and rebutted a false statement. As a parent, the extent of "intervention" I would take would turn on what "angry" looked like; the context of how my son delivered the statement; and a comparison of how other students are treated in disciplinary situations.

My personal opinion is that wilfully ignorant people should be allowed to make themselves look foolish after a fair, private heads-up. The teacher would have earned more respect from her students by admitting the statement was false, but that's a lesson I'd let her learn for herself.

What is to give light must endure burning.