FireLance
Legend
Oh gosh. So many possibilities, but I'll be generous and suggest that he might have trouble visualizing the scene.I just don't understand why he's having such a problem with this.
Perhaps to him, when he hears the word "rock", he doesn't see how it could be dangerous because he's thinking of a piece of stone smaller than a fist, instead of something roughly the size of a bowling ball.
Mind you, I think (although I have no practical experience either way) that even a relatively small (say, fist-sized) rock could kill (or say, smash the skull of an animated skeleton) if it hit a vital area and was thrown with sufficient force, e.g. by a half-orc fighter with an 18 or 20 Strength and probably not-too-bad Dexterity, too.
He might also be taking the approach that if such a large-sized rock had existed, the DM would have mentioned it. Or, he might take issue with another player simply declaring that such a rock existed instead of asking the DM whether or not it did, thereby infringing on what he sees as the DM's sole prerogative of defining what exists in the game world. This is more of a playstyle clash.
Or, he could be trying to impose his preferred version of reality (which may or may not be congruent with actual reality; see above) on what is essentially a shared fantasy.
Frankly, from the tone of his email, he sounds like someone who takes his gaming waaaay too seriously for me to have fun playing with him.