What caused Atticus to become a potential subject of discussion in the schoolyard, when he hadn't been before?

At the beginning of Chapter 10, Scout laments about her father's inability to play, his old age and uninteresting occupation. She compares Atticus to the fathers of her peers and mentions that Atticus possesses no unique talent or ability that would arouse any admiration from her friends at school. One day, a rabid dog named Tim Johnson staggers down the main street of Maycomb. All of the neighbors lock themselves inside their homes and Sheriff Tate arrives with a rifle. Tate hands the gun to Atticus and Atticus reluctantly takes it. Atticus then proceeds to fire the rifle, successfully killing Tim Johnson instantly in one shot. Scout and Jem are in awe of their father's marksmanship abilities, and Miss Maudie tells them that Atticus' nickname used to be "Ol' One-Shot." Scout comments to Jem that she can't wait to brag that her father's the best shot in Maycomb to her friends in the schoolyard, but Jem tells her not to. He reasons that if Atticus wanted them to know about his talent he would have told them, but Atticus never said a word. Jem looks up to Atticus and wants to remain humble like his father which is why he tells Scout not to brag.