When you pulled the spark plug and cranked it over, did it have slight compression/suction when you tried to hold your thumb in the plug hole?
If so, it might be a stuck valve.
if not it prolly "done blowed up" as they say in nascar.
What ever happened, it is not good.
Operating rotating things without lubrication has disastrous and costly effects.
a scored cylinder & piston, galled connecting rod and crankshaft amoung other things.
if done @ operating speed, it most always results in a "window" in the side of the block which you can observe the carnage without disassembly of the engine.
Either way, the minimum is removing the head for inspection as Jon suggested.