The boss is suspicious of George and Lennie and upset with them for arriving too late to work a full day.
The work slips that George and Lennie have received clearly state that they were to start work in the morning, as the boss makes very plain - along with his anger. When the boss looks at the work slips, he says, "It wasn't Murray and Ready's fault. Says right here that you was to be here for work this morning."
George says that the bus driver refused to drive all the way out to the ranch and that he and Lennie had to walk ten miles to get to the ranch. The boss seems skeptical at this, but accepts the story. He becomes fully suspicious of George and Lennie when George speaks for Lennie. George lies (again) and tells the boss that Lennie was kicked in the head by a horse when he was a kid and that is why Lennie cannot speak for himself.
After this interview is completed, the boss does not speak again to George and Lennie and in this way treats them as just two more ranch hands. The ranch hands generally are treated as mere labor - made to work hard at a very physical job, but fed and allowed something of a weekend at the end of the week. Though the ranch hands share some camaraderie, occasionally playing horse-shoes together, the men are largely depicted as socially isolated and economically exploited.
Steinbeck frames the desolation of ranch life by having George and Lennie comment on how different their lives are and having the other ranch hands comment on how unusual it is for two men to travel together. The hired hands have no personal stake in the ranch’s operation and, for the most part, no stake in one another’s well-being.