Ah , well, on HN you ARE supposed to go for the steel-man. And the steel-man happens to be closer to reality here, more like:
"We gave our agent a harness and put it inside a test environment and told it to keep hacking at an objective within that environment until it solved it."
'cept it turned out the container environment had a few flaws -which it always will- and the agent deemed it easier to escape out and try a meta-approach.
Partially this is possible because, -intelligent or not- the agent 'sees' the world differently from most humans. Mind: It's not like there haven't been any famous 'hacker' cases in courts where eg someone just incremented an HTTP GET parameter or something.
Also, partially it's because if you give the agent a loop, it simply has nothing better to do than to keep trying in ever more creative ways. If the environment is easier to crack than the target, it'll crack the environment. Consider the case where the objective is subtly broken, such that it is impossible to solve. Now breaking out is virtually guaranteed to be the easier task.
ps/edit: While this sort of issue has been predicted for some time now, a lot of people have been dismissing the predictions as science fiction. It's good to have an actual failure now while stakes are low. Generally people don't mandate life-boats until there's an actual Titanic to point to.