How does Scout's innocent perspective bring light into a dark situation in chapter 15 of To Kill a Mockingbird?

In Chapter 15 a large, threatening mob descends upon the jailhouse, intent on lynching Tom Robinson. Such lynchings were all too common in the South in the first half of the 20th century, so sadly there's nothing unusual about this scene. Atticus does his best to hold the men back, but they're determined to have their way.
Scout is in the midst of all the enveloping disorder. She looks at the men and doesn't recognize any of them. Then she notices Mr. Cunningham, father of Walter, a boy she goes to school with. Scout knows about some of the legal work that Atticus has done for him, so she starts talking about it. Mr. Cunningham is completely taken aback by all of this, and doesn't seem sure how to respond. The mood soon changes. Scout's innocence has diffused a potentially lethal situation, and soon Mr. Cunningham gives a signal to the rest of the men to go back to their cars and drive off.