What does Fan Shengmei’s joke to Yingying mean in Ode to Joy 2?

It was the one I saw selling watermelons. Did the programmer take a bun home in the end? If so, then the punchline to the joke lies in the way programmers think. In programming, if a certain condition is met, a corresponding command is executed. If it is not met, it goes to the next level. So from the programmer's point of view, the result is to buy a steamed bun when you see a watermelon seller. It’s not what we ordinary people understand: when you see a watermelon seller, buy another one