How does Beah develop a sense of credibility as a junior lieutenant in the description of the "Rambo" battle scene?   

Beah recounts his experience in charge of a small strike force of boys. He and Alhaji emulate moves from the war movies they have watched as they attack a village. The squad kills everyone in the village, impractically leaving no one alive to carry supplies back to their base. Beah sends Kanei and Moriba back to base; the two boys return with the corporal, some soldiers, and several civilians to carry the supplies. Because of this raid, Alhaji acquires the nickname “Little Rambo.” Lieutenant Jabati nicknames Beah “Green Snake” because he does not look dangerous, but he is deadly when he wants to be.