Why is Gretel surprised when she looks out the window?

In chapter 4 of The Boy in the Striped Pajamas, Gretel gets the opportunity to look out of Bruno's window, and the view is very confusing to her. The reason Gretel is so confused is because she has never seen a sight like the one she views out of the window. Gretel sees a community made up of only males, living in squalor in one-floor huts in an area with no greenery. She struggles with her lack of understanding, stating at one point, "I don't understand. . . . Who would build such a nasty-looking place?"
Gretel and Bruno have grown up in a fairly affluent lifestyle. They live in a large house, the family employs a cook and a maid, and the children attend a good school. They are not used to being around a community where people are struggling like the ones outside the window. But Gretel is uncomfortable with this lack of understanding and feels a need to explain what she is seeing. The author states, "She was twelve years old and considered to be one of the brightest girls in her class, so she squeezed her lips together and narrowed her eyes and forced her brain to understand what she was looking at." While Gretel is confused by what she sees because it is so unknown to her, she still wants to understand it.

In chapter 3, Bruno laments about their new home at Out-With and mentions to Gretel that the children he saw do not look happy. Gretel is initially confused and ends up following her brother to his room, where there is a window that overlooks the concentration camp. At the beginning of chapter 4, Gretel follows Bruno into his room and is surprised to see numerous people of various ages behind the fence. Both Gretel and Bruno are confused at what they witness and Gretel asks where the females are located. Gretel then tells her brother that she thinks they have moved to the countryside because there are no buildings that resemble a town or the city of Berlin. However, Bruno challenges her assumption by asking Gretel why there are no animals in the countryside. Both Bruno and his sister have no clue that they have moved to the largest concentration camp under German control and the people they are looking at through the window are Jewish prisoners.