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I would guess the argument would be that the copy was never actually sold; it was licensed. In fact, the judge seemed to jump through quite a few weird hoops to "prove" that. And since it was licensed, not sold, there is no right of first sale (because something that's licensed isn't sold), and if there's no right of first sale, then what's in the EULA doesn't contradict it. I don't agree, but I'd guess that's the argument.
Also, as someone else pointed out, this is the 9th Circuit... they get overturned a lot. Although so does every other Circuit Court (the Supreme Court doesn't tend to take on too many cases it feels were judged correctly, so more than 3/4 of all cases the Supreme Court takes on end up overturning Circuit Court decisions), but the 9th Circuit decisions just seem to be a bit crazy at times.
Well, AutoDesk clearly sold something. In the court's view, apparently, they sold a license rather than a copyrighted work.
In other words, it seems that the court is inventing a new kind of intellectual property right that expands and largely obsoletes copyright.
In this new interpretation, the use of software is governed by a license of more or less unlimited authority, where "use" is defined to include redistribution as previously governed by copyright.
EULA is the new copyright, this license is what you are buying when you procure software, and purchasing the license implies consent.
The license can be any otherwise legal contract, and the U.S. Congress is extremely disinclined to intervene in the terms of private contracts.
This is a creative end-run around the legal framework and judicial precedents of copyright. Copyright is irrelevant, because now we're exchanging licenses rather than works.