> ...and the sandbox hosts did not have internet connection either.

No, they did.

From [0]

> To gain access, the models identified and exploited a [bug in the Artifactory] registry cache proxy. With this access, our models performed a series of privilege escalation and lateral movement actions in our research testing environment until the models reached a node with Internet access.

If the sandboxes' network was airgapped, the only thing on the network with Internet access would be the router that sits between them and the Internet... and that router wouldn't have any services that listen on the airgapped network. Instead, they had at least one Internet-connected host on this "airgapped" network running a bigass pile of code, which -like many bigass piles of code- had at least one RCE in it.

If the software running on your machines can use anything other than Sneakernet to get data to and from the Internet, those machines have Internet access and are not airgapped. [1]

[0] <https://openai.com/index/hugging-face-model-evaluation-secur...>

[1] ...and -personally- I'd argue that if data can flow out from the systems to the Internet via Sneakernet, that ruins the airgapping. There are so many ways for a clever adversary to hide their communications. In this specific situation, this communications path isn't really relevant... but for many-to-most of the ones where you're bothering with the huge hassle of setting up airgapped systems it is.