What is the meaning of the story’s concluding action and dialogue?

At the end of "Everything That Rises Must Converge," the mounting tension that Julian has worked so hard to build seems to dissipate when his mother begins to enjoy the antics of the black woman's son. Julian had hoped to antagonize her into learning something by sitting with the black woman but "the lesson had rolled off her like rain off a roof."
To Julian's horror, when the no-nonsense black woman and her son begin to leave the train, Julian's mother insists that she will give the boy a penny. When she attempts to do this, the woman explodes with rage. It is unclear if she hits Julian's mother, but her fist "swings out with the red pocketbook."
Julian's mother is in a daze, when she finally gets to her feet, she can only say "home," and begins walking in the opposite direction of the Y, their original destination. Julian originally seems to believe that she is simply being dramatic and insists that they wait for a bus, but when she asks for her grandfather to come get her, he realizes she is having a stroke.
Julian's anger at his mother is simply a manifestation of his anger at the world. The "world of guilt and sorrow" is simply a life without his mother, something he was far too bitter to ever imagine. When she was in the early stages of suffering her stroke, walking along the sidewalk and repeating the word "home," Julian's mother wasn't talking about the house in which she and Julian lived, but the time in the past where the child and woman would have seemed grateful for her "condescending pennies." In her dying moments, she longed for the reality around which she could wrap her head.