What is the twist at the end of the story "Thank You, M'am"?

After Roger's attempt to snatch her pocketbook, Mrs.
Luella Bates Washington Jones has several surprises to spring upon him in the Langston
Hughes short story, "Thank You, Ma'm." The large woman first subdues Roger--putting him
in a half-nelson--and escorts him back to her apartment, where she makes him wash his
face and comb his hair. She then shares her meager supper with him--ham and lima beans,
and half of her ten cent cake. After they have eaten, Mrs. Jones goes to her purse,
which she has left out on the table (almost daring Roger to take it), and she presents
him with the biggest surprise of all: ten dollars for Roger to buy the blue suede shoes
he so desired.