> But looking closer, I actually suspect it’s not AI, the author just integrated LLM-isms into their style.

I think his native/first language is Russian -- em dashes are widely used (e.g. most definitions start with it, look at any Wikipedia article), quite a lot of people learn how to type proper em dashes and do so even in casual chats (a bit of self-proclaimed elitist sign).

edit: actually switching languages on Wikipedia and it almost seems like some USSR influence -- Ukrainian, Belarusian, Georgian, Azerbaijani, Kazakh, Uzbek and Tajik language pages start with em dash. Turkmen, Kyrgyz and Lithuanian uses eN dash. Armenian, Estonian and Latvian don't start with dash.

For non-ex-USSR countries/titular languages I found only Polish to start with eN dash.