My Mac has everyone in the families music on it. We have a playlist each that we sync to our various devices.
Since iOS7, all the music I've ever purchased from iTunes is now on my phone, not just my single playlist.
That wouldn't be so bad if the purchased music wasn't dominated by all the rubbish that I've bought for my kids.
I think it's just streaming, but it's still really annoying because my car shuffles between all the songs on the device by default.
Edit: Daryl's suggestion to turn off "Show All Music" in Settings got rid of all the purchased songs I hadn't played. Ones I was foolish enough to play remain firmly stuck on the phone.
Furthermore, these songs cannot be deleted by swiping left to reveal a delete button.