Why does the narrator find Doss's words about the old man unbelievable?

The narrator finds Doss's Words about the old man unbelievable because they suggest a level of empathy and care for others that goes against Doss's tough and unfeeling exterior. The narrator is surprised by the revelation of Doss's hidden depths, making it difficult for him to reconcile the new information with his previous understanding of Doss's character.