Nah, models can be fine tuned and trained on anything. Common consumer products like ChatGPT and Gemini have particular styles, very polite and helpful, but there are models trained to be combatative, models trained to write in the style of shakespeare, all sorts of things. Someone could train a model to reply to posts in the style of HN comments and you’d probably never know.
If you're just now thinking about it in this context, then you're about two decades too late.