This gentleman built his own home on wheels and needed a non-electric water heating option. The copper coil thermo-siphons the water.
I stared at the photo for a few moments, wondering why the piping seemed to be swapped. I thought it made better sense for the lower water outlet to be placed at the bottom of the pot so the colder water is heated first, siphoning upward and back into the pot. As I flipped through his photos, I found that he said the same.