In Boyne's The Boy in the Striped Pajamas, how does Shmuel exhibit heroic attributes?

Shmuel is the little Jewish boy discovered by Bruno within the fence of Auschwitz. Shmuel demonstrates heroic attributes by being kind, brave, and loyal during his time as a prisoner in a death camp. First, Shmuel is kind because he never discredits or vilifies Bruno's father. For example, Shmuel tells Bruno that he doesn't know of any good soldiers. Bruno quickly protests, "Except my father" (140) who happens to be the executive officer of Auschwitz and is probably pretty intimidating to Shmuel. Shmuel doesn't agree or disagree with Bruno about the Commandant, which is a kind and heroic act because he could have told his German friend how he really feels about all Nazi soldiers. Also, Shmuel could have told Bruno about all of the despicable things his father does inside of the fence, but he doesn't. Shmuel probably realizes that it isn't right to destroy a boy's image of his father.
Next, Shmuel is brave when Lieutenant Kotler catches him talking and eating food with Bruno in the kitchen. Bruno denies knowing Shmuel. This denial leads Lieutenant Kotler to tell Shmuel that he will have a discussion with him later about what happens to little boys who steal. Shmuel could have thrown Bruno under the proverbial bus at this point and called him out on his lie. However, the following happens:

"Shmuel nodded and picked up another napkin and started to polish another glass; Bruno watched as his fingers shook and new that he was terrified of breaking one. His heart sank, but as much as he wanted to, he couldn't look away" (173).

Unfortunately, Shmuel probably knows well that there would be no justice or mercy given by revealing his friend's secret, so he bravely finishes polishing the glasses and accepts his fate. 
Finally, Shmuel is loyal to his friendship by not holding a grudge against Bruno after the kitchen incident. When Bruno apologizes for not sticking up for his friend in front of Lieutenant Kotler, Shmuel does another heroic act:

"Shmuel smiled and nodded and Bruno knew that he was forgiven, and then Shmuel did something that he had never done before. He lifted the bottom of the fence up like he did whenever Bruno brought him food, but this time he reached his hand out and held it there, waiting until Bruno did the same, and then the two boys shook hands and smiled at each other" (175).

Not only does Shmuel forgive Bruno, but he doesn't mention the consequences that he probably suffered at the hands of Lieutenant Kotler after he polished the glasses that day. Again, Shmuel's strength of character extends to heroic spheres because heroes never brag about what they face; they simply endure.