I'd wager it is almost certainly real humans, just not engaging authentically i.e. paid trolls, at least until the cost of generative AI falls bellow troll farms.
If you bother to spend a couple of minutes looking for it, you'll quickly stumble upon a high volume of posts unmasking LLM-powered bots, which even respond to prompts to clear previous prompts, output their own prompts, and even generate content on-demand.