The Deliverance isn't a true story. It's a made-up tale that might incorporate some common themes or scenarios, but it doesn't have roots in actual happenings.
The length of DB mangas differs. It depends on factors like the story's complexity and the author's vision. Some might run for just a few volumes, while others could have dozens.
In the 'Deliverance' story, the banjo boy is a rather iconic and somewhat menacing figure. He is a local boy in the Appalachian region where the story takes place. His banjo playing is an important part of the atmosphere of the story, creating a sense of unease and otherness. The character represents the cultural clash between the main characters from the city and the rural, more primitive culture they encounter in the wilderness.