Front tire blowout - definitely a scary scenario. I'm glad you and the ranger did the investigation... otherwise it would probably have been written up as excessive speed and there would be a call for ticketing more cyclists (they never catch the really dangerous ones).
Those threads that come off the casing overlap are nothing to worry about. Rotten fibers in the side wall are a real warning sign.
I always caution people about heating up their rims on the descent, doesn't sound like this was the case here.
And a bike shop owner told me wholesale cost on new tires has gone way up (like 30%) so stock up now!