I think the same thing that happened to us happened to them. I was with a group of about 7. We rolled to the stop. The front guys yelled clear, car coming fast. We stopped. The car coming fast slowed and stopped even though they didn't have a stop sign. A car from the other direction never stopped. It does get confusing when this happens. I dislike when cars give the right of way even though they clearly have it. Ride defensively and take precautions.