I have to admit that I would've loved for it to be a hoax, but I'm not seeing it. If it were a hoax, I don't see Andy coming out on some internet site. He'd want something with a BIG stage, and his appearance would be the capstone of the evening.
No, he'd do this. Let people stew in confusion for a while, then burst on Letterman.
He would show up as a waiter at the Friars Club.
A few entertainment biggies and comedians would recognize him...Then he'd disappear again.
That would be more his style if it were a hoax.
No way anything as tawdry as the internet.