He was working on the pipelines going through the Alabama and Louisiana swamps. A lot of the worksites were only accessible via swampboat. Some know-it-all carpetbagger inspector/regulator/investor (not sure his specific role, but he was from the North and acted like he knew what everyone else should be doing) showed up at the jobsite and irritated just about everyone there. So at the end of the day, the workers conspired together to arrange for him to miss the last boat back to civilization.

He wasn't there the next day, and no one ever heard of/about/from him after that.

Despite the times, absolutely nothing racially motivated there. They just judged the guy by the content of his character and found him wanting. Seems a bit steep to justify manslaughter, though.