It doesn't, it refers to the idea that Christ cast out demons because he himself was a demon. Why would Satan cast out demons? He wouldn't, they were cast out because whether the demons wanted to go or not, Jesus as the Son of God (who was acknowledged by the demons) had absolute power over the demonic forces of the Devil.
Third Sunday of Pentecost
Pericope
Gospel Reading
Luke 11:14-23
Synoptic: Mark 3:20-30