Mistress Mysteria felt that this guy was a burden and she knew that she could dominate him and make him stop being one. She had tried to give him time to do it by himself but she did not manage. So she had to come up with a different way to do things and that is how she was able to facesit him and let the humiliation he felt do the work for her.
Madam Mysteria is a strong woman and she knows how to wrestle. This guy was proud and was bragging and she got fed up of it. She had to put him in his place and she did so using her facesitting fetish. The poor guy was shocked at what she chose to do to him and that is how she managed to torture and to humiliate him and above all, shut him up.