Consider an alternative hypothesis? In your hypnagogic state, your brain actually produced an image based on what she described to you, then reordered the chronology of events so that it seemed to you like you imagined the image before she described it. Not too dissimilar from deja vu.
It's well known that brains can sometimes reorder the chronology of events, especially if they occur within a short time window.
I was thinking even simpler: Maybe she started talking about the orange ball earlier, but he was asleep (or mostly asleep) at that point, and so started dreaming about it. Then he woke up at the last bit of the story.
Interesting. I've had several strange experiences in the last year which could be explained this way (as I have no other way to explain me "seeing the future"). In one example, my brain told me there was a 5 euro note under a chair at a cafe, and then I looked, saw it and picked it up. In another example, I saw a fruit had fallen from a tree and imagined an older man come and pick it up and then look up at the tree. This exact thing occurred 10 seconds later.
Other weird experiences include living in a new country and having at least 20 instances of deja vu there within a short time (not of having been there, but just random moments I had seen before in my head).
It's well known that brains can sometimes reorder the chronology of events, especially if they occur within a short time window.