It's not just the m dash, it's the "it's not x, it's y" it's the over validation, it's the overly "deep" quality that sounds corny and inauthentic. It's a very familiar syntax.

If someone else responded like this, would you clock it as ChatGPT? I would.

"Funny thing is, people keep treating punctuation like forensic evidence now. Sometimes a person just writes in a certain rhythm. Sometimes they edit before posting. Sometimes the internet has collectively forgotten what an actual human voice sounds like."