Continuity mistake: When Boss and Charlie are crossing the flooded main street (before rescuing the dog), Boss is holding his shotgun pointing up into the rain in one shot, then in the next shot (from a different angle), it's pointing down, then up again and so on.
Continuity mistake: Near the beginning of the movie, after the rainstorm, Charlie and Mose are digging and flopping around in the mud to get the wagon out of the hole. They are both covered in mud. As soon as they get the wagon out of the hole, Button says "Here comes Boss". As Boss rides up, Charlie is removing his gloves, which are now dry and free of mud.
Continuity mistake: When Boss and Charley hide in the Marshall's office to wait out the storm, they pull the shades on the windows. After Baxter's men come in and Boss and Charley lock them up in the jail, the shades are back up on the windows.
Continuity mistake: Charlie's dog, Tig, is referred to once as a "she" and once as a "he". In the scene where Charlie and Boss are heading back to town to find Mose, Button indicates the dog wants to go too. Charlie refuses, saying "She's got the heart ... she ain't got the legs." Later, in the scene where Charlie buries Tig next to Mose, he says, referring to Tig, "... he was more his dog than mine."
Continuity mistake: When Button is picking his feet Robert Duvall tells him to move downwind. After he does so, you can see many cattle on the hill behind him. The scene cuts back to Duvall and Costner. Seconds later cuts back to Button and the cattle are gone.
Answer: I believe he is the one being chased by the townfolks, after the gunfight is over.