The situations aren't really comparable. We're talking about sending a request from a computer to a publicly available API endpoint that Open AI would rather you didn't, and then using the data that endpoint sends in response.
(Somewhat tangential, the "networks as a 3D space you travel around in with locations you visit" analogy does more harm than good. It's not what's happening and it results in muddled thinking.)
Something being accessible does not mean you're authorized to access it. Someones house being unlocked doesn't mean it's okay for you to enter. Authorization is the key part here and you likely can be convicted under the CFAA[1].
Again, I don't think the analogy holds—no one is entering anything. A better analogy would be someone standing outside your house and asking you to pass a book to them through the open door, which you then voluntarily do.
(Somewhat tangential, the "networks as a 3D space you travel around in with locations you visit" analogy does more harm than good. It's not what's happening and it results in muddled thinking.)