This guy was a compulsive masturbator and this mistress felt that she could dominate and humiliate him. She had to do it for her own fun and she chose to teach him a lesson in a way that he would not forget. That is why she went out of her way to use her dry hands to jerk him off so that he would feel pain. And that was after she had facesat him with her jeans.
This mistress used her nice ass to facesit this guy but she did not stop at that. She also jerked him off at the same time as she facesat him. It was to have fun at his expense and see how he would handle the two things she did to him simultaneously. He felt both pain and pleasure and he was shocked but at least it was not as bad as he had feared it would be.