Where is THAT from that's not how the movie ended.

you must have never seen the movie then, because that's how it ended man.

I saw a different ending where the devil gets sick of listening to them rock, and shoots a lightning bolt which deflects off of Jack's guitar breaking off the devils horn and the Jack grabs it and does the spell that sends the devil back to hell unless he gets his horn back and Jack and Kyle turn the horn into the Bong of Destiny.

It's from the music video for the song "Tribute".