ACS,
There is no diagnosis going on here, obviously!
You call it what you will, I'll call it what I will, it's subjective.
But that isn't what I am saying! I think they are different and one of our jobs as parents is to try to tell the difference. You make a good point about kids needing to distance themselves when situations are too bad for them to be able to cope in other ways. Kids who do that should have their situation addressed. I just don't want every instance of a child daydreaming to be thought of as a sign of abuse. Perhaps I misread your post.
I am saying that a child who can entertain himself when needed (say a long car trip or while waiting his turn in line) without needing to resort to outside entertainment (like electronic games) is different than a person who is checking out to protect themselves from traumatic situations (physically or emotionally). Kids who are abused in various ways do check out and that is bad. Spending 6-8 hours a day being completely left out and bored is neglect which is a form of abuse. If your kid is doing that, then find out what is going on.
But having a kid who looks out the window and daydreams while driving down the highway or waiting in line for lunch, that just doesn't seem like a problem as long as there are plenty of opportunities for engagement in most of the rest of the day or other signs of a problem.
