Why did Fan Guangyan kill Pan Yangyang?

Fan Guangyan posted information online to recruit temporary workers. Pan Yangyang saw the information and went to work. After working for a day, he was paid in the evening. Fan Guangyan saw Pan Yangyang's fashionable dress and asked, "Have you ever had a part-time job?" Pan Yangyang angrily slapped Fan Guangyan twice. Fan Guangyan pushed Pan Yangyang to the ground in anger. Fan Guangyan, who lost his mind, accidentally killed Pan Yangyang. It was too late when he came to his senses, and then he burned his body and hid it by the Black Water River. Later he surrendered.