I can't speak for him, but I do believe that was his vision for the future. However, what he shipped (Facebook 3.0) was native. He was long off the product before the frankenstein HTML5/Native Facebook app shipped.
You might have been right about his vision for the future of the Facebook app. I do recall a blog post by Joe in which he mentioned something like that he didn't like developing native apps for iOS anymore due to certain policies by Apple.