Why are the narrator and the young boy who had lost his face considered outsiders by the others?

The boy with the black handkerchief, whose face had been injured, was not at the front long enough to receive any medals. The narrator says that, at first, the other boys were polite about he and his own medals. But when they found out that he had received medals simply for being an American, their demeanor with him changed. 

I was a friend, but I was never really one of them after they had read...

The boy with the black handkerchief, whose face had been injured, was not at the front long enough to receive any medals. The narrator says that, at first, the other boys were polite about he and his own medals. But when they found out that he had received medals simply for being an American, their demeanor with him changed. 

I was a friend, but I was never really one of them after they had read the citations, because it had been different with them and they had done very different things to get their medals. 

In the end, the only things that the narrator and the four other boys shared was that they were all somewhat emotionally detached from their experiences in war and that they all went to the hospital. The narrator and the boy with the reconstructed face had only been wounded. They do not have the same evidence or experiences of bravery that the other three boys had in their efforts during the war. 

The narrator calls the other three boys "hunting hawks." He finds more in common with the remaining boy (injured face) because "I thought perhaps he would not have turned out to be a hawk either." 

The major and the three Italian soldiers with medals symbolize the Hemingway "Code Hero," the man who illustrates courage and bravery. The narrator and the boy with the injured face are outsiders because they have not proven themselves to be this kind of hero, a "hunter," or an accomplished soldier.