That's not what happened. You can make up all the scenarios you want to justify stealing.
It was a private campground, his neighbor could have waited to see if he was coming back, or contacted the office.
Some of the rationalizations to take someone else's property are pretty creative.
Even if I had the situation you described, and found some things on a site I pulled into, I would just set the stuff aside, and see if they came back. After a day I would give it to a park Ranger, or someone else in charge.
What if the people before me had an emergency, and couldn't get back right away. I was raised to not take anything that didn't belong to me.
True story:
My father was a small business man, grew up during the Great Depresion, and the most honest person I have ever known. One day he over charged a customer something like a dime. As a boy I worked at his store, and that day, on the way home, my dad stopped at the mans house to give him his dime back. The look that man gave my father was pretty cool. I often think about that day, and it was over 50 years ago. My dad taught by example, and I have always tried to live my life the way he did.