I like to imagine that they didn't play a single note, they just went up on stage and trashed everything and the crowd went ass wild over it.
This is another game that we only owned the demo to, but we had some good fun with it! The point of the game is to manage a rock band, simple as that - create the band, create the songs, design the covers, decide on tours, all that stuff. And it's pretty good fun, honestly! I've seen some video review channels pick this one up, and they all seem to have pretty fun with it, too.
The voice acting is decent - they hired some good professional voice actors for the Swedish dubs. I can't remember where we got the demo from, but it still had the swearing and drugs despite the slightly childish character design and Swedish voice acting, which probably tricked quite a few parents into giving their kids this game. Which is funny as hell.
So yeah, it's probably a fun way to spend a few hours.