Goddess Lena did not want to have a slave who was attracted to her sexually. She was uncomfortable when this slave checked out her ass regularly and she could see desire written all over his face. That is why she had to put an end to that nonsense. The mistress chose to slap the shit out of him and make him do things the right way. The hard slaps that landed on his face made him stop that habit.
Goddess Lena was frustrated by this guy because he was not focusing on what she wanted him to focus on. And that is why she chose to dominate him and make sure he learned to focus better than he had been doing. The frustrated mistress not only slapped the shit out of the guy's face, but she also kicked him in the face to achieve what she wanted from him.