.... how does he and the son appear in a family group photo with Julia that she pulls out of the book her father-in-law gave her at the end of the film?
Also, how does Sting show up at the wedding banquet if she meets him after the car accident?
-- What would Joan say? --
The family photo could indicate that she has once more entered the other world or maybe it's just a comforting delusion.
I'm guessing Sting was just there by coincidence and probably didn't meet her. Alternatively, it might've been a 'glimpse' into the other world. Notice how he's initially in the garden but when Julia goes there, he's gone.
The whole film is very ambiguous.