Play Music app is activated by Words With Friends Let me just say that I have used both apps independently for a couple of years.  I have a Galaxy S III.  Recently I replace it with same due to battery issues.  I don't know if the replacement is new or used.  I play Play Music and I also play Words With Friends.  Recently I have had strange occurrences with the phone.  When I play Words With Friends the last song I listened to on Play Music will start playing.  The App is NOT running until I start playing WWF.  I think this is probably a unique situation and I'll just wait until the phone is eligible for an upgrade next month.
Go to Applications Manager > Play Music and clear defaults.