AI reliably uses em-dash, normal people writing generally do not, even if they know what they are, because it's more complicated to insert them. So yeah, there's a reason it's known as a "tell."
>it's more complicated to insert them
Word automatically replaces the hyphen with it when between words surround by space — because it's the correct punctuation. I sincerely hope you don't believe it's too complicated when the task is done for you by Word — the most popular word processor. Additionally — just to test it out — long pressing hyphen yields the character on my phone. This has allowed me to effortlessly pepper this reply with slightly extended — and a touch controversial — horizontal lines.
Just because your writing style doesn't use em dashes — a rule taught to literal school children — doesn't mean it's not "normal."
Finally, I am sorry to report that my use of the em-dash has not allowed me to transcend humanity and become a cyborg — though I will return with a follow up post if I suddenly sprout a Serial port.
You're generalizing inappropriately across cultural boundaries. Is the author of the OP article an abnormal human? Does "normal" mean "of average writing level"—is it now socially acceptable to ostracize and bully people who write well?
Because, when you're accusing people of being bots (like the HN parent related), that's a seriously unpleasant form of bullying. It's dehumanizing, quite literally. (When you write with sincerity, you pour your own humanity into your words; what does it mean to deny that?)