From what I've seen while loading into Itunes, it's the length of the tracks and order that identify the particular album. If it can't identify it, sometimes it'll ask you to enter the information (and presumably the next person who loads that set will get an automatic ID). It did make one mistake for me, IDing a worksong album as some random pop album, but it's been remarkably accurate. So - maybe someone else loaded the same album and labelled the tracks.