How did Bod and Scarlett become friends in The Graveyard Book?

The Graveyard Book was written by Neil Gaiman in 2008. It is a bizarre story about a little boy named Bod, a human boy who literally grew up in a graveyard. Bod arrived at the site as a very young child when he strayed away from a man named Jack who murdered his parents and sibling. Bod became an adopted child of Mr. and Mrs. Owens. Bod grows up around a strange group of people, most of whom are dead graveyard dwellers.
In the story, the graveyard is a historical site and nature preserve, so local visitors often visit to appreciate the history and beauty. When Bod is still very young, he interacts with and becomes friends with one of the visitors, a young girl named Scarlett. Bod explains the ghostly figures and haunted environment of the graveyard to Scarlett. They both go on a hunt for the graveyard's oldest ghost.
After they both finish this adventure, Bod and Scarlett make their way back to the park, where Scarlett’s parents are searching for her. They find her and then leave, and then they subsequently move away. That is the second to last time that Bod sees Scarlett. Scarlett returns to town with her mother after they moved away for some time. At first, she doesn't remember Bod or her experiences. There comes a time when she gets lost and inadvertently runs into the graveyard where she used to play with him. The memories come back to her mind, and her friendship with Bod becomes reignited. Their shared interest in discovering the unknown made them befriend each other. It was seemingly by random chance that they became good friends while they were together at the graveyard site.