Why do Camera and Smilin call Granny "aunty"?

In "Blues Ain't No Mockin Bird," two men are on Granny's property "makin movie pictures." They are referred to by the narrator as Smilin and Camera based on what they are doing. When Granny comes out to the porch, one of the men approaches her and begins to tell her what they are doing. However, Granny interrupts the man by saying, "Good morning." The man seems to realize he is being rebuked by Granny for his lack of manners because he hangs his head before responding to her. He then says, "Nice place you got here, aunty." He refers to her as "aunty" again when she makes it clear that she does not want him on her property taking pictures. The man calls her "aunty" in an attempt to be familiar and easygoing. However, he shows his ignorance and lack of respect when he thinks that by calling her "aunty" she will allow him to continue. Granny lets him know that she is not related to his mother. "Aunty" is often a derogatory and disrespectful term used to refer to black females.