The correct response is: Her familiarity allows her to invent an otherworldly explanation for events she can easily predict; Nuttel’s unfamiliarity makes him believe this as truth.
In "The Open Window," Vera’s knowledge of the setting and the family’s background allows her to craft a convincing story about the supposed tragedy that befell her family. Nuttel, being unfamiliar with the setting and the family dynamics, is easily deceived by her tale, which ultimately leads to his misinterpretation of the events that unfold.