project84 (rahn)
+1y
jmz is on the right path. I work at a tire factory. As far as I know, there hasn't been a retreaded passenger tire in years. I say passenger tire, because we manufacture "regular" tires (cars, trucks, vans, SUV's) and we also manufature "truck" or semi tires. Tread separation such as that is more common on truck tires than on common passenger tires, but it does happen. Possibly the way jmz put it or another possibility is low air pressure, etc.
Sorry to hear of your damage, but truthfully you got pretty lucky. I've seen tread come off and beat the livin' $hit out of a bedside or rear quarter on a car!