Apparently people in the production had stated that they were given Dean's work to base Avatar items and markings on.
Even if true, so what? You can't copyright the idea of a floating island, and the Hallelujah Mountains were heavily enough inspired by actual mountains in China
as to make any ripping off claim silly and completely baseless in legal terms at best.
is right. All this guy's doing is making himself look like an asshole to anyone who might consider hiring him in the future.