It seem to be differents in definition of rural road-
Rural road, so that means (to me) the kind of road where it is about a car and a half wide (where one car has to pull of the road to allow an other to pass, usually paved with pitch tar and gravel), so if wingnut was on the far right hand side and the horse was on the left eating grass the could have easily passed within 20 feet of each other (a rural road in the chiacgo area is probally not this narrow, but in tenn., miss. and ala. they are, and I just now looked and saw that wingnut is from chiacgo area)
At 20 feet, this is still close enough to spook a horse espeically if the horse is 'green' or spooky and coming from behind

All that I ask is that you annouce yourself as you came up to a horse (especially from behind), if does not harm you any and might prevent someone else from being harmed.
I would hate from this to happen to someone I know while they where riding their horse along the road and it could have been prevented simply by someone annoucing their presents.

Enjoyed the debate, have a great day