I thought the accent was a decent job of 'genteel southerner who is massively racist'. I thought the point of it was that you have these so-called gentlemen who are monsters, and it played well to parallel 'gentleman' Bellamy who almost killed his friend and his friend's daughter.
On one of the behind the scenes, they said they filmed the West in Romania iirc.
I'm not questioning historical accuracy. I'm saying it was just a lot of plot; they didn't need it. Plenty of people out West were still racist. They're talking about faraway events in Tennessee or wherever, and I don't know if a non US audience really grasps the context. He could have just been a wanted outlaw who didn't think the war was over.
It's fair for Fogg and his development. No way he was preparing to shoot the guy, but as soon as 'coward' came out, I think Fogg would have done it. Abernathy knew at that point, which was why he dropped his gun. Abernathy was the real coward there though. Big 'confederate' captain probably never had to fight on equal footing. He talked a good game, but Fogg wasn't backing down at that point and he caved.