It sounds as if the crank sprocket kept turning while the crank pulley was held stationary?? The ruined sprocket and pulley would have been where the two inside faces were turning on each other?? From memory of my timing belt replacement, and consulting my FSM (not very detailed at all), it appears the crank sprocket sits against a rear flange on the crank shaft and is indeed sandwiched between this flange, an outer flange and the crank pulley. The torque transfer is from the key on the shaft to the pin and the torqued friction of the crank bolt. There is no taper on the crank shaft. I don't think there is very much torque to worry about on the crank pulley (the pin being location and some torque transfer) and I don't know how it could have seized, other than one of the accessory items seizing. Can you turn all the driven accessories? Could the A/C compressor have seized with the clutch engaged? I would think if the water pump seized it would have made a terrible noise first?? Maybe someone else here can offer more info.