Ernesto's actuality is best left unexamined, I think.
Maybe he's a wormholian who can slide between realities (I knew kids like this).
Or maybe he's a projection of the zeitgeist. Whatever, he's good for laffs when used sparingly. For what it's worth, below is my favorite Ernesto appearance. Which is available in the first CdS book at Amazon for only $5.20. So that's what it's worth.