What did the brothers find strange about Cameron's car when they inspected it in the novel, The Lost Man?

Upon inspection, Nathan noticed that "nothing was wrong, and that in itself felt very wrong indeed" (18). The car had plenty of gas, it was stocked with food and water, and it started without problem. The only thing out of place were the keys, they were coiled perfectly over the seat - to Nathan's memory he had never seen Cameron do this.