How is this a humorous story?

In analyzing "The Open Window" we should not lose sight of the fact that this is a funny story. None of the characters laughs, but that is part of what is funny. Fifteen-year-old Vera not only has a vivid imagination and a mischievous nature, but she has a wild sense of humor. Her whole purpose in making up the story about the three men who died while hunting is to create the reaction she evokes in the hypochondriacal visitor Framton Nuttel.
Framton grabbed wildly at his stick and hat; the hall door, the gravel drive, and the front gate were dimly noted stages in his headlong retreat. A cyclist coming along the road had to run into the hedge to avoid imminent collision.
Except for giving the approaching hunters a look of "dazed horror," Vera remains completely deadpan as her elders wonder why their strange visitor left in such a hurry. But Vera must be laughing on the inside. In fact, she may be having a very hard time to keep from laughing out loud.