Explain the irony in "The Open Window."

Saki's short story "The Open Window" is ironic because it ends in an opposite way from what we expect. Early in the story, we think that Framton is visiting the home of an older woman who has psychological issues as a result of a great tragedy suffered a few years prior. The woman's fifteen-year-old daughter tells Framton that her father, two brothers, and pet spaniel exited through this "open window" in the house and disappeared on a hunting trip; tragically, they were apparently lost in a bog and presumed dead. Vera says her mother cannot cope with their deaths, so she leaves the window open every day, expecting them to return.
When Mrs. Sappleton finally enters the scene and makes references to the return of her husband and sons, Framton is disturbed by what he presumes is the extent of her denial. As Mrs. Sappleton looks toward the window and talks about expecting their return, Mr. Sappleton, the boys, and the dog all re-enter the house. Framton is so upset by this surprise that he immediately leaves. Vera basically leads him to believe that those family members are dead to scare him when they return. She made up the whole story.
Instead of learning that Mrs. Sappleton is mentally unstable and delusional, we learn that her daughter Vera has a gift for making up fantastical stories that sound realistic. She does the same thing when she explains to her mother why she thinks Framton left in such a hurry. She invents a story about a horrifying past experience Framton had with a dog. The story ends with the line "Romance at short notice was her specialty." Saki uses the word "romance" to mean the capacity for telling creative and imaginative stories. The story is ironic because the story's conclusion does not reveal Mrs. Sappleton's mental illness but Vera's storytelling skill.