It’s not saying it can’t remember. It’s saying it doesn’t have the ability to do what it did.
> "No, I did not write that poem."
Literally what the comment is saying. It wrote something and can't remember that it wrote something. Remembering that it wrote something is fundamental to answering the question of if it wrote something. Otherwise, how would it ascertain the difference between someone whose style mimics that of ChatGPT output and actual ChatGPT output? No memory means no certainty.
It's different from asking it if a comment was generated by an LLM, in which the response heavily leaned on the word "appears". However, LLMs have no understanding of what it's given, it's all just tokens and Bayesian inference.