Stop it with the fake boos.
The audience responds negatively. They don't like the whole setup. Mel B hits "X" the instant she see him. She's not having it.
But he wins over the audience and the judges get the joke. It's a fine well done joke. Simon Cowell gets the humor immediately.
He comes back for a second audition and by then all the audience is entirely won over. They know what to expect and they want to see more. I think he progresses to a third round. If you care to see them, the rest come up in sidebar over on YouTube.
I think his imitation is hilarious.