The final paragraph, or really the last two paragraphs, reveal a change in the tone--so this is a great question to ask. It's where things become less breezy and more contemplative.
Throughout the rest of the story, the narration is informal and conversational; we understand that it conveys the thoughts of not just the baffled Marin but also the dismissive police who question her, filtered through the voice of a seemingly indifferent narrator.
Short, conversational statements characterize most of the story. "That's right." "She likes to dance." "Nothing in his pockets."
But then, those last few paragraphs of the story reveal a change: the tone becomes serious and sensitive as the narrator describes how Geraldo's family will never hear from him again and never find out why.
Longer, more dramatic sentences characterize this last paragraph, like this one: "The ones he left behind are far away, will wonder, shrug, remember."
To sum up, the tone in this very final paragraph is contemplative and mournful because it addresses the themes of the story--the sad fate of an undocumented worker in the US, the nature of a life of anonymity as an immigrant, the bleak indifference and open hostility exhibited in the US toward illegal immigrants-- while the rest of the story's tone is practically peppy in comparison.