I can think of two possibilities:
1-manufacturing defect. How old was the tire? Any warranty still in force? It could also have been damaged in shipping.
2-road damage. Anyone besides you drive the car? Others can be 'forgetful' in reporting hitting something on the road.
I'm thinking 1 more than 2, road damage seems to typically cause sidewall blow-outs, not what you had. But maybe something sharp was hit, causing a slice across the tread. Photos would help.
As for tire construction, 'radial' means the cords in the carcass of the tire run from bead to bead, and would separate as you describe. However, the belts that tires also have do not typically run in that direction, and would have to be sliced to fail as you describe. Google 'radial tire construction' for lots of diagrams, such as the one shown above.