It’s called discipline and setting a standardshe can teach whatever she wants to teach. that post in the op is not teaching. it's telling her student of the rip how they will be punished for using what may be common sayings and telling them they are unintelligent for saying them. major difference.
plus wasting precious "teaching time" giving them a list of 30 phrases to remember not to say only in her class when they can actually be learning something.
It’s an academic environment
It’s time to learn and not socialize
Talking wasting time that’s a 3 min read