He has a solid claim - he was going to shop it around to publishers, but the public dissemination of the material kinda devalues the work. Additionally, it's still his IP. This should be a slam dunk.
I don't see how it devalues the subsequent completed movie though, seeing as both of his last two films were leaked (on purpose?) online far in advance and did great business. I do think his rant was completely out of proportion. First world problem, rich guy problem, get a hold of yourself.