The hooks only work when the tire is inflated. A deflated clincher on a hooked rim is still going to come off if you keep riding it.
You either believe that DeGent's tire spontaneously blew off the rim, causing the crash (and rim damage occurred during the crash) - or you believe what Vittoria and Zipp have concluded, that he hit a rock, which damaged the rim causing the tire to deflate, which then came off the rim.
On either system, you're probably in a world of trouble if you have a spontaneous blowout at 50mph on an alpine descent. Pretending that hooked rims are going to save you in this situation is silly.