How does the narration affect oskar’s credibility in this excerpt?

Below is the excerpt:

The average person falls asleep in seven minutes, but I couldn't sleep, not after hours, and it made my boots lighter to be around his things, and to touch stuff that he had touched, and to make the hangers hang a little straighter, even though I knew it didn't matter.

The answer is "His efforts to heal render him earnest and genuine."