There is a way. You can message the player and enquire after their previous username. If they refuse to respond then you can be assured that they haven't enough respect towards you to tell you, their supposed friend, who they are.
~msgScore~: +0
32. TwinkleRose,
I got confused because someone removed me from their friends list I think but they were still on mine. however I couldn't join their table as it said they wish only their friends to join. it confused me.