Agree, saying that an HN comment is AI-generated just because it has an em-dash, is like saying a Twitter/BlueSky/etc post (or WhatsApp message, etc) is AI-generated just because it ends the sentences with a period.
"it looked like a real message but the dot at the end gave it away"
There are similar opinions with artists too. Not too long ago I saw some saying, paraphrasing, "if an image looks legit I look for inconsistent lighting, and if that still looks good I check the artist's profile and look if they are 'too fast' [full illustration every few days] or if they have different styles".
I haven't seen anything like that with code, but I wouldn't be surprised if someone said that human-written code is actually AI-generated just because the structure looks weird to the reviewer, or because it has some "what" comments (instead of "why" comments; both have their place), or things like that.
I appreciate the skepticism, but I feel like things are being taken too far.