She was probably teasing him. To say that he was a peach meant that he was very cute and sweet, while a "heart arsonist" was to describe a girl who liked a boy very much. She would even become "arsonist" because she liked him and pursue him very hard. If you also like this type of story, I can recommend to you the ancient romance novel "Jiuniang". The emotional entanglement between the male and female protagonists is also very exciting. I hope you like my recommendation, Mwah ~😗