Why was the maniac of Gadara not a Gentile?
He was not a Gentile because he was a Gadarene, meaning a descendant of the tribe of Gad. Gad was one of the Israelite tribes that settled on the east side of the Jordan River. Though he lived east of Jordan, his ancestry was Israelite, not Gentile.
Les explains that during Christ's earthly ministry, Jesus directly dealt with only two Gentiles: the Canaanite woman and the Roman centurion. When people object that the maniac in Gadara must have been a Gentile because he lived east of the Jordan River, Les asks what the first three letters of the word Gadarene are: Gad. Therefore, the maniac of Gadarene was a descendant of the tribe of Gad, which was an Israelite tribe that lived on the east side of Jordan.