Final answer:
The family learns of Lupito's action through the rapid spread of rumor, which indicates the close-knit nature and efficient communication within the community.
Step-by-step explanation:
The family finds out that Lupito had killed the sheriff through the fast and efficient spread of rumor. This method of communication is likened to telephone wires, highlighting the swift and inescapable reach of news in a tight-knit community.
Unfortunately, the snippets provided do not contain the specific moment where the family discovers the truth about Lupito, but they suggest a setting where news travels quickly, and the impact of such events is deeply felt by the characters involved.