It’s rooted in the tradition of American machismo and braggadocio. Hyperbole is a huge part of the American oral tradition. You go to any small town in the Southern US and the old timers will have some tall tales that beggar belief and they will tell them too you as if it were the gospel with no winks or nods.

I think Devil Went Down to Georgia is supposed to be viewed as a boast by Johnny himself. “I’m a really good fiddle player.” “Oh yeah?” “Yeah, this one time I beat the Devil himself.” “I told you once you sonofabitch, I’m the best there’s ever been.”