The question about why he was passing through is a very old police question, especially in rural areas. “We don’t get many strangers in these parts.” In their experience, the answer lets them know whether you are up to no good or not with a single question.
There have been many times and places in US history when an area would just get overrun with transient scoundrels, and if there is just one or a few lawmen, they prefer to nip such problems in the bud.
While lots of movies and TV shows depict someone loudly asserting their rights with police officers, that is the big city way. In rural areas, police expect good manners, and usually respond in kind.
I need to move where you live.. The cops in my area (rural) do not have good manners. I was stopped close to home once- The Deputy said “I stopped you because I thought you were going to run.” And another Deputy stopped me close to home and asked: “How long have you lived around here?” As if that meant anything. I told him “I moved here before you were born.”