That’s not so crazy, is it? “Civilian” is used in the thought experiment to refer to an expected level of training, experience, and equipment. You wouldn’t reasonably expect a “civilian” in this context to have an RPG or an attack aircraft. The clear point of the thought experiment is “would a civilian be able to kill an armored vehicle with the level of training, experience, and equipment that would reasonably be expected of a civilian in this context?”