They aren't, they're one of the people who latch on longstanding and neutral syntax (em-dashes, "it's not $foo") as a proof of LLM text. I don't blame them because HN has a lot of people trying to pass gen AI stuff as their own, and you need quick heuristics... but I'd encourage people at least do it right. Pay for Pangram or something.
Or as the new saying goes
"HN: Professionally identifying 230% of posts from 2017 as LLM generated".
That said Panagram is trash for the opposite reason. Not that some people talked like LLMs before LLMs, but now a lot of people talk like LLMs because of LLMs.