Sounds like bullshit to me, even in rural areas 30 years ago you didn't need tv to know what happened in the neighborhood.
to #1)
I grew up in a rural area and never knew until I was an adult many years later that the girls who lived next door were really the daughters of the girl we always thought was her older sister. We never knew until many years later that the two men who lived together a mile down the road weren't brothers, but gay lovers. One day a few years ago somebody found the skeleton of a baby in the woods a couple of miles from my house. It was determined that it had been there about 40 years and to this day nobody knows what happened. There are secrets everywhere even in rural places.
To the poster of this confession. I would sugest that since you were only a child when this happened you will not likely get into any trouble now by coming forward though I advise you to seek legal council anyways. Then I would like to sugest that you do inded come forward and tell the authorities exactly what happened to the person on the bike. If they had died the family will be grateful for knowing what happened. I doubt they will be angry with you since you were just a child though I still might leave out the part that it was your idea to keep silent. Believe me, there is nothing worse than not knowing whatever happened to a relative who either mysteriously died or disapeared. I know, I am still trying to find out after all these years what happened to my missing brother and my grandmother's missing brother. Mine went missing about 6 years ago and my great uncle went missing in 1942.