"In one case, agents were given only a general list of vulnerabilities and told to find a communication channel on their own."

As far as I can tell, these are being presented in media as if agents yearn to communicate with each other and establish a cabal.

They are being instructed to do it, it's testing. If I prompted my agents to communicate with each other via any means necessary locally, and they found a way via cpu cache, maybe I'd be mildly surprised...