Guitar Hero: On Tour is, in general, an inherently solitary activity. There are more barriers to playing with friends, most notably that each one needs a DS and a copy of the game, and it is impossible for more friends to watch your performance. So you end up playing alone with your headphones on. It's only natural for the only Guitar Hero that can be quickly hidden in a backpack.
But On Tour: Decades does have interaction in mind -- with other On Tour owners, in its song-sharing capability, and of course the multiplayer gameplay. And the way this ad suggests such a meeting will occur is not through the party setting, but by chance meeting. If you want to find another Guitar Hero player, go out on tour!