Most likely he freed himself from someones pen. They have an amazing adaptablility. If he finds a snack (scratch that has bounced off the fence) or a place for food and water and no pestering dogs/cats etc, he may just stick around. He may even come and go. On occasion I have lost some and assumed they had fed a coyote or a red tailed somewhere, then a year later they show up, or when the snows get deep and I have better snacks than what nature has to offer. You never know.
