Why does Scout tell Uncle Jack he does not understands in To Kill A Mockingbird?

Scout told Uncle Jack that he doesn't understand kids at all, in chapter 9 when Uncle Jack came to apologize to Scout after her fight with Francis. Scout said that when something comes up, he should try to model Atticus: try to hear both sides of the stories and decide who is the innocent one and who is the guilty one and treat them accordingly rather than close the head around one idea.

She said it is best to keep the mind open to other conflicts and possible outcomes even when you are sure on one of them.