please help me diagnose what happened here
this is off of my friends jdm/first gen b16 engine
it jsut died on him when accelerating (not hard either)...pulled the plugs and this is what i saw (this is the only one that looked like this)


when we looked down the spark plug hole all we saw was one chewed up cylinder....we also turned the engine over with all the plugs out and it sounded smooth
so what do you all think happened???
thanx in advanced