You know, it probably was good chicken back then. Nowadays between fecal sores and small takeaways on a mission to serve something actually decent, KFC is pretty much a last resort.
Remember that: Fecal. Sores. Their factory raised chickens sit in their own shit and get infections. The evidence of which is visible on the meat.
to keep things in perspective, i think it would be fair to say that kids were more active in those days than today, and that chicken doesn't look as bread encrusted as todays KFC.
If memory serves, the original KFC was actually decent food. I don't think it got the "fast food" treatment until Pepsi bought it.
When I was a kid we would get Kentucky Fried Chicken every once in a while, and we always had to wait. It was never sitting under gian heat lamps drying out and turning into rocks.