I couldn’t follow the description events well. Dunno if it was the writer or my comprehension, but if I gather it correctly, the cars ahead might have been going slow because of the cyclists. This happened to me once, feeling impatient behind a car doing well below the speed limit and not seeing cyclists ahead due to a gentler curve in the road, so I went left to pass and saw the cyclists when I did, then backed off. I realized what I did wrong and ever since them I try to be more cognizant of why a driver might be going slow before I make any decisions.
Much of the time on country roads, it's because they're getting close to home.
Many don't pop their turn signal until they're right on top of their driveway.
Perhaps drivers who slow down because of cyclists should turn on their hazard lights, to get the traffic behind them to slow down as well.