I don't believe the author is trying at all to represent a form of punishment in our protagonist's mental condition. (Perhaps self-punishment, in the form of guilt feelings.)Rather, I think it's a sad illustration of what often happened to (and does happen to) boys who are too young to be faced with such things. That's why I think the fishing scene is so brilliant, as I mentioned before. It's a perfect metaphor. A pastoral, innocent scene: Two happy, clueless friends fishing and excitedly discussing joining up, when one of the boys fishes up a horror from beneath the water. This is especially great foreshadowing, considering that we later deal with his mental state, and that water is often used as a metaphor for the unconscious mind. And what do they do? They push it back beneath the surface. Well, what else can they do? It terrifies them. There are marvelous layers of emotional, and thematic, depth in this scene.

Plus, I do think it's obvous he feels guilt, despite the fact that he couldn't have done anything for his friend. People often feel such guilt when a loved one dies. Guilt and helplessness. It doesn't make sense, anymore than war does, but it happens. This is a finely crafted piece of fiction, delicate, sensitive, and insightful. It's about ordinary people placed in extraordinary and terrible circumstances. It is not, I think, a story meant to be analyzed in broad, simple sweeps. As in any truly great piece of fiction, there is more to it than first meets the eye.