Had they notified him with a web page that his mac address wasn't welcome it would have been a different matter altogether.
What Aaron did was the equivalent of trying a different laptop to see if things resumed working.
But Aaron kept on evading every single countermeasure MIT was putting in his place. By the time you get to going into a wiring closet, you have well passed the point where you know you are no longer welcome on the network.
The law cares very little about what tools you use, and they care a lot more about the actions you do and why you do them.
Aaron wasn't an idiot. He knew MIT was trying to keep him off. It wasn't just a network error.
As for whether banning they MAC address conveys revocation of the license. The precise form of the communication is irrelevant, it's about whether it can be expected to get the message across in context. Do you think Aaron didn't know, after the various measures MIT took, that he was no longer welcome on the network? If he did know, then the message was conveyed.
You're basically attacking a straw man. You're acting like he was charged for trying to access the publicly-available MIT home page, getting a 404, and trying again with a different laptop to see if the problem was on his end. That's what would be analogous to your "calling someone who isn't answering then trying a different phone" example.