An accident
As Jim was driving along the road, he saw that there were some aggressive tire marks left on the side of the road. Marks that would signal that a car had run off the road and onto the side for at least a moment. He looked at the patch of green next to the tire marks as he drove by it, but saw nothing.
He shook his head and thought that maybe it was just nothing, someone probably just swerved off the road for a moment and lost control. There was no car crash or wreckage so he was sure that everything was fine. They got off the main road shortly after that and parked their car.