Mr. and Mrs. Buttington are a couple who are familiar to the narrator through Fanny, who has shared many details about them. The narrator's greeting suggests a friendly relationship and indicates that they are meeting for the first time or reconnecting.
In the context of the story, the mention of Fanny highlights her role as a relay of information and perhaps a link between the narrator and the Buttingtons. The casual tone and the quote reflect a typical social interaction in a middle school setting, emphasizing the importance of friends and acquaintances in the story.