How do you define a user, and how do you define online?
If the forum considers unique cookies to be a user and creates a new cookie for any new cookie-less request, and if it considers a user to be online for 1 hour after their last request, then actually this may be one scraper making ~6 requests per second. That may be a pain in its own way, but it's far from 23k online bots.
AFAIK it keeps a user counted as online for 5 or 15 minutes (I think 5). It’s a Woltlab Burning Board.
Edit: it’s 15 minutes.
That's still 518.400 requests per day. For static content. And it's a niche forum, so it's not exactly going to have millions of pages.
Either there are indeed hundreds or thousands of AI bots DDoSing the entire internet, or a couple of bots are needlessly hammering it over and over and over again. I'm not sure which option is worse.