a lot of applications auto convert -- to an em dash

and a bunch of phone/tablet keyboards do so, too

I like em dashes I had considered installing a plugin to reliably turn -- into em dash in the past, if I hadn't discarded that idea you would have seen some in this post ;)

And I think I have seen at lest one spell checking browser plugin which does stuff like that.

Oh and some people use 3rd party interfaces to interact with HN, such which do auto convert consecutive dashes to em dashes.

In the places where I have been using AI from time to time it's also not supper common to use em dashes.

So IMHO "em dash" isn't a tall tell sign for something being AI written.

But then wrt. the OP comment I think you might be right anyway. It's writing style is ... strange. Like taking a writing style from a novel and not any writing style but such which over exaggerates that currently a story is told inside a story. But then fills semantics of a HN comment. Like what you might get if you ask a LLM to "tell a story" for you set of bullet points.

But this opens a question, if the story still comes from a human isn't it fine? Or is it offensive that they didn't just give us compact bullet points?

Putten that aside, there is always the option that the author is just very well read/written, maybe a book author, maybe a hobby author and picked up such a writing style.