i agree with being able to kill the engine both ways...ignition and or kill switch.
i have always set my planes up to be a fool proof as possible (hey, Dad was USAF veteran so i learnt).........
in this case, a kill switch would have been the best choice, and from what i have seen it is a smart choice for the flyer.
funny thing is though, i watch Bob all the time at the field and he is very cautious in tuning his engines to run right. this one just got away for some reason.