Lady Dominika had beef with her slave because her slave was not behaving the way she wanted him to. That is why she chose to shit on him and make him realize that she was not one to be messed with. The mistress made sure that he also licked her asshole clean before she felt that the punishment was enough for him and she let him go. He learned his lesson.
Lady Dominika was right and this guy was wrong but he was adamant that he was right and it pissed her off so much that she had to find a way to punish him. She did not want him to take advantage of her to mess up and so she used her shit to punish him and that is how he ate her poo and he learned his lesson cruelly.