That's clearly Pupkin's imagination. Think about all the times he was day dreaming, it was EXAGGERATED, a lot, and now read the last lines of the script (which, by the way, different from the original draft where it is clearly not day dreaming, here is instead not that obvious..), after stating that the biography has been sold for a million (a million!) dollars, and that a movies will be made on it soon, and that "he and his people were weighing attractive offers":
And now, ladies and gentlemen the man we've all been waiting for, and waiting for.
Would you welcome home please television's brightest new star The legendary, inspirational, the one and only king of comedy! Ladies and gentlemen, Rupert Pupkin! Rupert Pupkin, ladies and gentlemen! Let's hear it for Rupert Pupkin! Wonderful! Rupert Pupkin, ladies and gentlemen! Rupert Pupkin, ladies and gentlemen! Let's hear it for Rupert Pupkin! Wonderful! Rupert Pupkin, ladies and gentlemen!
You get it.. This is no different from when, during the movie, his teacher is thanking him because.. he changed their lives.. :D