Oh of course the skit was made up. But the clips from Bush's speeches weren't made up. Yes, the skit picked and chose the pieces of Bush's speeches they wanted, but that doesn't mean he didn't say those things. He can't speak in public, has terrible grammar, repeats himself, and in general sounds like an idiot, without anyone else's help. "If you don't stand for something, you don't stand for something." Duh. "I don't think anybody anticipated the breach of the levees." Duh again, everybody except him anticipated it.
While the skit is fake, you really can't argue the point that Bush does sound like an idiot.