Come on! Today i pay for the premium version and go offline and didn't work, i just find out that doesn't work if you don't downloaded the songs you want to hear. Aren you kidding me?! Why you don't give that kind of information!!!?? That's important information.
Yes that's how Offline works. You need to download the songs first, how would you be able to listen to them offline otherwise? Spotify streams music over the Internet. Spotify has over 30 Million songs and you can't have that much music available offline.