Legally, I think it's also true that an open door looks more like an invitation to enter (and it's different from burglary to simply poke your head in the door, see if anything is wrong, and not breaking or taking anything)
If an API is served on a public network and your client hits that API with a valid request which returns 200 (not 401) and that API is shaped like an open door, such that no "knock" or similar magic or special protection-breaking incantations were required in order to obtain "the access" ...
Then would you concede it's not actually like a burglary, but a bit more like going in through an open door to see if everyone is OK? (It sounds like that's more precisely what happened here, I'll admit I haven't read it all...)