Assuming it was cleanly in gear when you released the clutch, I doubt if this shortened the life of the engine much. The stress from this was probably felt most by the clutch plates, belt, pulleys, rear tire and spokes. And, having done this at least once myself, the shoulders and wrists probably took some of the negative g-forces also.

Surely you pulled the clutch in real quick, right? Man, Ive downshifted "wrong" & made the rear tire slide & the engine tach up,,