Did u check the clearance on every blade specifically and carefully?
Seems likely that if clearance was checked just generally, which is all that is usually done, one blade could have been closer to the rad than the others and u would not have noticed.
It is obvious that the blade deflected forward from the force of moving the air, then hit the rad, because u said: "it let loose while revving the engine". Next time, keep it under 10,000 rpm