Mistress Nyx needed to teach this guy to do things her way and that is why she chose to teach the guy a painful lesson. She had to ensure that he would never forget it and that is why she put him in his place by spitting on him after she had tied him up. She had a whip on her hand ready to strike if he did not toe the line.
Mistress Nyx was inconvenienced by her driver and she did not like it. She had to make sure things changed and that is why she went out of her way to dominate him and do it in a way he never expected. He was spat on and turned into a spit slave. He nearly puked but she told him that if he did, he would have to drink it too.