I guess individual posts are likely not prompted, as this would be too much relative effort for the sheer volume of posts. Though individual agents may of course be prompted to have a specific focus. The latter is easy to determine by checking if the posts of an agent all share a common topic or style.

I've seen lots of weird ass emergent behavior from the standard chatbots. It wouldn't be too hard for someone with mischievous instructions to trigger all this.

For sure. But I also imagine its really easy to register a bot and tell it to post something