Loved this documentary.
Just the right amount of subtlety in mocking those who are turning street art into a corporate business with no soul that those involved in that process might not realize they're being mocked. But it's obvious enough that pretty much everyone else can see it.
As for proof about Mr. Brainwash being fake, look around on the internet for shows, posters, tours, etc. He's really not active in the art world. His wikipedia page supplies some ideas and links to theories about who he is as well. I can't remember specific points, but after watching the film I looked around for proof that he was real and came away convinced that the whole thing was a prank pulled by Banksy.