It certainly should, but it also should be obvious that this was not information that he was authorized to have, and he was prosecuted for intentionally scraping it after noticing the misconfiguration - not for making an HTTP GET request.
The idea that a GET request is like asking a clerk for an item under a counter is appealing, but doesn't really work because granting access is not the same as granting authorization. Authorization requires intent, and an HTTP server is incapable of intent (at this point in history, anyway). The fact that the server can be misconfigured and is fundamentally incapable of realizing it means it makes a lot more sense to think of it as the counter rather than the clerk, and items with 403 responses as items that are under a glass counter. For this same reason, the FOIA request example doesn't work either. A human (or many of them) processes that request.
Additionally, the items he took were not items the store sells, they were clearly items the store should not have out in a public place (so yes, the "store" is absolutely not blameless).
In light of these observations, I think a better analogy is this:
A man walks into a store. He spots a binder on the back counter, just close enough he can reach it without actually stepping behind the front counter. It contains a printout of the store's mailing/cold-calling list that they use for [whatever silly purpose]. The clerk is busy elsewhere, so he starts flipping through it page by page, taking a photo of each one with his smart phone.
Now, I'm still not sure what I think of the legality or morality of the situation, especially when you try to factor in intent. I'm also not a legal professional of any kind, so I know even less about what a court would think about all that. But I do think that these details are relevant, and leaving them out of an analogy creates a false impression that there's nothing even debatable about the situation.
Edited to add: FWIW I do agree that AT&T is very much at fault, mainly for the reasons phaus gave in the comment sibling to yours. I just don't think it is obviously the case that their guilt excuses the person that takes advantage of that negligence.