What she tells Scout about Boo Radley in this chapter is that she believes Boo is still alive. She says that he never comes out of the house simply because he does not want to. This is totally out of sync with what Scout believes.
Scout believes that Boo must be dead. Maybe the Radleys have killed him and stuffed him up a chimney. Scout can't believe that he would stay inside all the time just because he wants to.
What is going on here is the Maudie is teaching Scout not to judge people for being different.
In Harper Lee's To Kill a Mockingbird, Miss Maudie is stellar among the myriad characters as she is much like the children's father: she, too, is a genuine person who does not judge anyone whose shoes she has not "walked in," as Atticus often instructs his dear children. Unlike the "footwashing baptists," and Stephanie Crawford, the neighborhood "scold," for whom Miss Maudie is a foil, she does not entertain gossip or the disparaging of people's good names.
Miss Maudie's views underscore those of Atticus and furthers the bildungsroman motif as well as the motif of supersition with her influence upon the maturation of Scout and the dispelling of some of the superstitious beliefs that the children hold about the Radleys. Furthermore, she sets a good example for the children as her words and actions teach Scout not to prejudge people.
In the book "To Kill a Mockingbird" Ms. Maudie talks about the Bo Radley that she remembers and his family. She explains to the children that she could recall a time when Boo Radley was a little boy. He always smiled and had been happy. She explains to the children that many of the things that they have heard are made up stories. She goes on to tell the children about how religious the father, Mr. Radley, had been and the toll that had taken on his family. Her words and things that Jem and Scout have been thinking about result in Jem feeling stronger about Mr. Radley.