Insult: humiliation

In meaning, humiliation is humiliation, and humiliation is also three, so your teacher is wrong.

The dictionary is the most authoritative in Chinese, and there are only three insults in it.

Literally, insult is not a common word or something, so it can only be read three times.

Now some teachers teach dialects very seriously. Maybe it's because he's used to reading like this?

In a word, you are right. Correct the teacher's reading.