He doesn't cause those notes. That's the game presenting the song to him. If he didn't hit the notes flying down the screen at him it would just go "clunk" and you wouldn't hear the note played. Then the crowd starts booing and the word "failed" appears on the screen and they don't let you continue.
I've experienced this before, as you might guess.
You can see "50 note streak" appear on the screen a few times. The note count resets every time a single note is missed. Ellen was trying to explain how to tell what he's doing but it's hard to explain unless you've played it or seen it played a few times.