I never heard that. What I heard is that the demons were called legion because there were many of them (as an entire legion) in the person. And Jesus removed the demons from the man and put them in the pigs who then ran off and drowned themselves, as a lesson to us that Jesus has power over satan and has dominion over the creatures (the pigs) so it is a show of Jesus might and the power of God over the enemy. Satan prowls about the world seeking the ruin of souls so they are better in pigs than in people IMO on that last one.
Side note… God has an army of angels working for Him, but satan also has an army of fallen angels called demons.
Ephesians 6:12 For our struggle is not against enemies of blood and flesh, but against the rulers, against the authorities, against the cosmic powers of this present darkness, against the spiritual forces of evil in the heavenly places.