I know plenty of folks who take this stand (sorry), but I can't help suspecting that there are reasons that an author includes this and not that; reasons which the author himself needn't be conscious of, perhaps can't be. So, I tend to ask the same kind of questions as in the OP.
I'm not going to answer it, but I will tell you that reading is an interactive experience and requires both a writer and a reader. You bring something to the party too, you know, and that is interpretation.
It's not a test and there isn't any single correct answer.
You or I or anyone may not agree on the significance of any aspect of any story, but that would not necessarily mean that any of us were "wrong."
Enjoy the story as you find it. It is a gift (even though you have to pay for it).
Yes...it is even stated that Detta Walker was "born" when the brick hit her, and became more real after she "took the A Train." (Love that song - I'm not a huge Ellington fan but WHEW! Cat Anderson wailing away, has to be the best version ever!)