Symbolism, Imagery, Allegory
So, after all that pessimism and doubt, a naked dude with a halo comes and rescues the men from the beach. This guy has got to be an angel of some sort, right? He's got a halo for crying out loud. Maybe there really is some greater supernatural force in the universe looking out for these four men.
We can't forget, though: the guy might appear to have a halo from a distance, but in the end he just turns out to be a good Samaritan (and nudist, maybe)—a mere mortal. His presence is in line with the general nihilist tone of the story—what may appear as supernatural is, at a closer glimpse, nothing more than the ordinary. After the first failed rescue attempts, this realization redeems the men's faith in humanity and enhances their embrace of their fellow man. Hey, maybe this guy is the ghost of the French soldier from the poem; did you ever think of that?