I can tell an actual Southerner wrote this
There are several phrases in the movie which are specific to the way southerners really speak, as opposed to the way outsiders 'think' we speak. (the regular collection of cliches)
I don't have time to get into making a list now but maybe sometime I can come back and mention a few from the movie. One reason the lines are authentic could be because they used regular people in many of these roles. Just a thought.
Cheers