It's been a long time since I saw the movie but I didn't remember it being a nickname I thought it was his given name. I've never met anyone with that name in real life.

a family affection name that was picked up by friends of the child and carried out into the community and stuck. Sometimes the name is given by the community, example, My brother who my mother preferred to call William, was instantly named Bill or Billy when he started school. Southern nick names are as random as those from any region.