The Question and Answer section for All the Pretty Horses is a great resource to ask questions, find answers, and discuss the novel.
I think that MCCarthy is referring to the end of rural ranch life the way Grady's grandfather, and others during the era (1860's to mid 1900's) had lived.
Grady's mother plans to sell the ranch. Are you talking about his move away from San Angelo, or another section in the novel?
I think it might be because he looks different than the regular audience members and he is smoking a cigarette in the lobby.