Blatty's Bizzaro

Does anyone else find it passing strange that William Peter Blatty, author of the Exorcist, Legion, and the Ninth Configuration; Screenwriter of films such as Great Train Robbery & Omega Man, actually wrote this bag of crazy?
Don't get me wrong, I enjoyed the satire...but it seems an odd source. I can only shake my head in wonder. What an incredibly talented author.