Let's focus on the second part of the passage, because I think there's a lot more meat to this part in regard to the question.
The short middle paragraph describes the man he killed in very humanizing words. He does not describe him as an enemy or an animal, as depictions of "the enemy" often do. He describes him as a young man, short and slender. His reason for killing him is out of fear, which is generally not the idea we have when we picture soliders at war, fighting for their country. It is a less attractive idea to kill a man because you "were afraid of something". This establishes a moral complexity to the act of killing in war.
Another interesting snippet is his hypothetical idea of the man living, and continuing down the road. Again, he paints this picture in very humane terms. He describes him as having "shoulders slightly stoooped", likely fatigued from the long day's march and the constant stress of war. He imagines him "suddenly smilling at some secret thought", as if he is privy to the idea that fate has spared him, and he is allowed to "continue up the trail as it bends into the fog". The second half of this sentence, about the trail and the fog, could be a metaphor for the two men going down their own separate paths like ships passing in the night, having a huge effect on the life of the other, but not knowing where the other will go from there.
