At the end of The Lumber Room by Saki, how can Nicholas be considered a hero?

Nicholas is the protagonist in “The Lumber Room” by Saki. He is the main masculine character, and he exhibits cunning actions in the face of adversity, which, by definition, makes him a hero in the story.
Nicholas is a young child who proves to be wise beyond his years when dealing with the adults in his life. After he puts a frog in his breakfast of milk and bread, he is forbidden to accompany the other children on a hastily arranged expedition to the beach. When the adults do not believe there is a frog in his breakfast, he produces the specimen, which he put there himself. While the others go off on the excursion, Nicholas is left at home with his cousins’ aunt, who sees herself as the ultimate authority figure. As they leave, it is expected that he will be upset, but instead he correctly predicts that the beach excursion will be a disaster.
While the rest of the family is away, he is forbidden to enter the garden. The aunt is sure he will attempt to enter the forbidden space, so she spends her day on guard by doing menial tasks. Nicholas instead finds his way into the mysterious Lumber Room, where he discovers great “treasures,” all the while outsmarting the aunt. Eventually, the aunt falls into a water tank in the garden and cries for help. Using his ingenuity, Nicholas asks the aunt a series of questions, which outwit her. He exclaims she cannot be the aunt but must be the “Evil One.” He leaves her in the tank to be found by a maid.
When the others return, it is obvious that their day was an awful experience, and Nicholas did not miss out on anything. In the end, he had a great adventure in the Lumber Room, while the others, including the aunt, were miserable. Although he is a mere child, he uses his ingenuity to teach the adult aunt a lesson she would not soon forget; therefore, he can be considered a hero in the story.