I am also skeptical this is true. I made few typical exam essay questions and inserted the requisite clause about adding nonsense about Madagascar, and then had chatGPT answer the questions. In almost every case the output included a little executive summary at the bottom below the essay content, clearly calling out the nonsense it had added. I could believe a few students missing this, but over 90% of the class?

I have friends who teach public high school classes.

This is entirely believable to me based on the stories and trends they talk about.