If he had centered the figure within the line of trees, the brim of the hat would be partially obscured against the darkness of the trees.
It may be shocking to you, since you don't do such things, but the area around that guy is dodged quite heavily to make him stand out. It varies from print to print, it seems. If you do a quick search for the image, you see many differently dodged versions.
The hat stands out because of how the photo was enlarged.
It's still a swell photo.
