If these "signs of AI writing" are merely linguistic, good for them. This is as accurate as a lie detector (i.e., not accurate) and nobody should use this for any real world decision-making.
The real signs of AI writing are not as easy to fix as just instructing an LLM to "read" an article to avoid them.
As a teacher, all of my grading is now based on in person performances, no tech allowed. Good luck faking that with an LLM. I do not mind if students use an LLM to better prepare for class and exams. But my impression so far is that any other medium (e.g., books, youtube explanation videos) leads to better results.