Source of Bias

As we progress through this semester I have come to articulate something I have been mulling over for a while; that the difference between fiction and nonfiction have more to do with the reader's perception and experience than the "absolute truthfulness" of events.  Yet I find myself contesting myself.  One of my favorite quotes is on page 181, "It was a joy, for example, to watch the birds simply as birds and not for the significance they might have-whether they were a sign of good or evil, an opening of the pack or a gathering storm."  Every time I read it I feel a connection to the men, in my case experiencing a burden being lifted by not having to watch the clouds for thunderstorms.  Then I wonder if this was actually what they felt or just a literary device to facilitate my understanding and empathetic connection.  I try to rationalize it all by saying that it shouldn't matter, yet to me it still does on some level.  What is this pull from nonfiction?  It comes from our perception, when we pick up the book and it tells us it is nonfiction, but why?