Should it be possible??

Well you said stock fan! Is it possible it is a clutch fan!As the other guys stated it is possible to turn a non clutch fan by hand and also in the process turning the engine over if the belts are tight,are you sure the engine is turning over when you turn the fan.I would mark the balancer and see if it is turning when you turn the fan,and NO the timing will not be off just because you turned it by hand.When you turn the crank you are also turning the cam as long as the chain is installed!