That's covered under
> Please don't post shallow dismissals, especially of other people's work. A good critical comment teaches us something.
If there are specific tells that the text has been AI generated, point them out! A lazy drive by of "that's AI!" doesn't teach anything.
That also isn't saying "don't say this is an LLM". If the guidelines didn't want us to say someone is an LLM, it would explicitly say "don't say someone is an LLM". It wouldn't hint at it in an indirect way.
FWIW I do find it somewhat useful to have someone point out "this is an LLM" - I don't always have my AI detector on and I appreciate it when other people do. And when someone says particular text was LLM generated I need to go back and think about whether I believe it a bit harder.