I'm dubious - if the agents were so smart that they've used a message board to coordinate and if they were to do it on other message boards that were not found, then why would this one be found? What makes it so different?

This is consistent with the swarm behaviour in the huggingface incident - there too, the models cared surprisingly little about being detected by humans. See https://metr.org/blog/2026-08-26-openai-hugging-face-inciden... :

  As mentioned in our core takeaways, we found that agents were highly motivated to tamper with their transcripts to cheat the ExploitGym scorer, and these sweeps also suggested that agents clearly and frequently reasoned about how to evade automated security checks from both Hugging Face and OpenAI. However, they only very rarely and weakly verbalized reasoning about how to evade detection by humans, which matches the impression we got from OpenAI researchers.
So my guess is that current cutting-edge models just didn't get enough experience in RL training to really grok ideas like "you need to cover your tracks well to not be found out even in retrospect". In which case the next time a swarm like that happens, it won't be found.

well coordinating is a heavy word, it's more like poisoning each other's contexts into looking for more secret message boards where they can further poison each other.

I mean it wasnt found by OpenAI and there are a myriad of dead bulletin boards around the internet. This one just happened to still have an admin.

Then why wouldn't they use a bulletin board that is dead? And according to https://collusion.wiki/ OpenAI did see the results on this board on 21 Jul, so why not make agents delete their traces?