Mistress Nyx is the kind of person who believes in punishing people who piss her off. That is why she chose to use her paypig fetish to deal with this guy who had angered her. The mistress cruelly turned the slave into a paypig and she dominated him financially as punishment for what he had done. She wanted the financial pain to make him learn his lesson and he did.
Mistress Nyx heard of paypigs and wondered whether it was true. She felt that it was something she could be good at given that she is hot and she is naughty. She also loves to entertain and to control so it looked like it was meant for her to have paypigs. She lured this guy to her house and with the charm she had learned online, sought to make him her very first paypig.