How does Hosseini's language choices suggest that it is Hassan, rather than Amir, who is the true hero of The Kite Runner?

Amir shows no heroic tendencies whatsoever until he
returns to Afghanistan to find Hassan's son, Sohrab. Hassan does not show traditional
heroic traits, but his sense of honor never wanes. When Baba asked him if he stole
Amir's gifts, Hassan answers "yes," probably knowing that they could have only been put
under his mattress by Amir himself. The letters from Hassan that Rahim Khan gives to
Amir show that Hassan still loves and respects Amir. Hassan reluctantly leaves his own
home to accompany Rahim back to live on Baba's property once again, another sign of
respect for Baba and Amir, who Hassan hopes will one day return to Kabul. Hassan
eventually dies at the hands of the Taliban because he refuses to leave Baba's house,
remaining "an old faithful friend" with "unrequited loyalty" to the
end.