The tone of The Ransom of Red Chief is humorous. Authors use different types of humor in literature including, but not limited to: hyperbole, dialect, and understatement.
Hyperbole is using obvious exaggeration to create humor in a story. An example in this story, "a town down there, as flat as a flannel-cake". O He's overly exaggerating the flatness of the town by comparing it to a flannel-cake.
Understatement, on the other hand, is the opposite of hyperbole. The author creates humor by using understatement to describe the innocence of the energetic, mischievous, red-headed boy in the story. Sam and Bill underestimate the power and danger of the little boy they call Red Chief.
Another way authors use humor in literature is through dialect, the way people speak depending on the region where they live. When the boy says, "I was only funning", it's humorous, because it's not the way most people talk. It's unusual, so it's funny.