That sounds like a timing attack against the iMessage servers, probably also involving the unpatched client.
These researchers took a phone they owned and setup a situation where a server they controlled sent messages the phone interpreted as coming from Apple. Those messages were used to extract the key from the phone they owned. They then used that key to access an account they owned and were the authorized user of.
Is there a technical case of unauthorized access if they used a non Apple client to access the photo? Maybe. Did they establish the same pattern as Weev, accessing information related to many other users? No.
Not to mention giving the hack to Gawker before notifying AT&T, getting caught with cocaine, violating a gag order, and saying "I won't nearly be as nice next time" shortly before his sentencing.
No locks were broken - not even the weakest 1bit password. Weev only incremented a number of a public endpoint.
The prosecution in his case, as in Aaron Swartz's, conspired to use their legal enforcement powers to intimidate the innocent. They literally, knowingly, tried to charge people for things they knew at the time weren't crimes, because they had been "humiliated" by losing earlier.
(*Innocent of the charges at hand - questions of someone's "other" guilt are out of scope.)
The problem isn't that easy hacks can be criminal, it's that the punishments are out of line with the harm done.
And yes, a guilty-verdict and a one-cent fine wouldn't be too big of a deal. But ideally the courts just wouldn't even hear the case.
Weev took the data provided to him by his codefendant and gave it to Gawker.