The same way that you can look at someone's post history, skim it, and more or less understand what their deal is.

Most users on reddit don't have this diverse set of interests or posts. Most of them post on the same subs and repeat the same types of posts... ad nauseam. Most people, online, aren't much more sophisticated in their language use or POV or anything... than a bot.

Sure, 10 years ago you'd look at someone's post history and it would be all over the place, and they'd be writing detailed and nuaced paragraphics in lots of detail... but that's not what reddit is like anymore, or most of the internet really. God I remember when libertarians actually had decent theoretical argumentation to defend their viewpoints... and now it's just memes and cliche phrases repeated over and over.

Pretty easy for any LLM to parse a person who just incessantly posts about the same stuff over and over. And if it came across someone doing long-form explanatory stuff... it would just ignore that data since that doesn't fit the task LLM is designed to process.