Amazing that his core body temp didn’t give out. But he shouldn’t have discarded his boots: they can be held upside down as flotation devices. I recall the story of a Marine who fell off his ship, and used his training to survive in the water: took off his pants, tied the ankles shut and kept flapping them full of air to use as water wings.
We learned that technique when I took swimming lessons in middle school. We had to be able to jump in wearing shoes, jeans and a shirt (over our suits), strip, and use our shirt and pants as life preservers. That was for my “Advanced Swimmer” Red Cross card.