I don't have a specific chapter to give you, but it's definitely in there. It was when Goong Hwa first invited Sun Hwa into the bakery to try his goods, and in the flashback, there was a kid that might've been Sun Hwa, and he was bullying a blond foreign kid in the canteen: asking if him he liked bread since he was a foreigner, then the blond kid vomits. And then it flashes back to reality and Goong Hwa is asking if anything is wrong with the garlic bread he gave him because he was disturbed by the flashback.
Wait... in Sun Hwa's flashback, was he bullying a blond foreigner kid? What if it was Goong Hwa? But if it is so, what if Goong Hwa has some elaborate plan to get revenge on him... that might be worse than what his sunbae did to him.