I saw this video when he posted it. The fact he maintains he is "safe" and experienced is pointless. Any cyclist that travels at 60mph down that particular road is completely at risk; one bit of road debris/pothole, a car, a sheep, a momentary lapse in concentration, gust of wind. There is an endless range of things that, at 60mph, are impossible to counteract. As soon as any cyclist gets beyond about 20-25pmh on a descent, your facility to stop as safely as you can has evaporated.
You can argue 60mph is iffy for sure but 20-25mph? Even with my very modest efforts I can do that on the flat.
For me anything over 40mph feels quick downhill.