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.
Any idiot knows that you can't copyright an idea, only execution. That's what this is about - actual copying of multiple images/structures/markings and admission of same. Not an accident, not an homage, not a coincidence, willful wrongdoing. Something Cameron's done before and lost that lawsuit.