This guy was a loser and he had to get what was due to him. Mistress Nyx did not want to let him continue down the path he was on and so she had to use her boot fetishism to dominate him and put him in his place. That is exactly what she did to him and he was shocked at what she did. But she saw it through and made him cry in the process.
Mistress Nyx wanted to try boot fetishism on this slave because it was one of those things she had not gotten to try yet and she did not want to waste any time on it. So she went out of her way to dominate as well as humiliate this guy for it. He deserved it because he had pissed her off and she also wanted to try it on him so it was a win-win for her.