Yeah...there's nothing stopping you from exchanging a few songs between friends.
And besides that, it doesn't have to be the EXACT same file, just the same song that meets similar parameters. The tags have to be the same, and the length has to match up. That's pretty much it.
If the game were enabled to stream music to other players, it would count as illegal sharing of media, and would break several copyright laws in the process. Meaning, the developer (A one-man operation) would have a number of media companies all over him filing lawsuits.