This "emdash" and "double dash" discussion and mention is the first time I have heard of it or seen discussion of it. I've never encountered it in the wild, nor seen it used in any meaningful way in all my time on the internet these last 27 years.
And yes - I've seen that special dash character in word for many years. Not once has anyone said "oh hey I type double dashes and word uses that". No it's always been "word has this weird dash and if you copy-paste it it's weird", and no one knows how it pops up in word, etc.
And yes, I've seen the AI spit out the special dash many times. It's a telltale sign of using LLM generated text.
And now, magically, in this single thread, you can see half-dozen different users all using this "--" as if it's normal. It's like upside down world. Either everyone is now using this brand new form of speaking, or they're covering for this Claude code developer.
So yeah, maybe I've been sticking my head in the sand for years now, or maybe I just blindly ignored double-dashes when reading text till now. But it sure seems fishy.