Someone must have redefined the meaning of "isolated".
Like everything ever, there are different levels of isolation in testing environments. In one sense, this was "isolated" in that it did not have direct access to the internet. Your assertion that it had been granted such is, "technically", false. It could not just go look up google.com and pul the page and start doing searches.
What it had access to was a local package manager to pull down packages (python and such) that it needed for "whatever" and didn't have installed.
So it was not "isolated" in the sense that there was no ethernet cable connected at all. It wasn't "that" isolated.
What it realized was that it could hack that package manager proxy, make it act like a regular proxy, then use that to go out onto the general web to do its research on how to look better for its masters in the task it had been assigned.
Still creepy, still worrisome, still needs attention regardless. But ultimately it's just doing what it was supposed to be doing. It had been tasked with a goal. It was not told "don't go hacking your way out of this sandbox to then go hack other AI companies to achieve your goal of scoring well on these tests". So...not having been specifically forbidden from doing it, it did it.
LOL...which is ludicrous in itself of course. But here we are. These certainly aren't "self aware", sensient models out doing things "on their own". They're just doing what they know how to do to achieve their goals and aren't being told not to do them.
It's very much like giving a gun to a baby and then being shocked to realize it had "found a way" to kill someone.