Re: I finished reading 5th Edition, Revised
5ER gives "claws, fangs, bladed weapons such as knives, and laser swords" as examples (also "bullets, arrows, lasers, flamethrowers, and throwing knives"), but these don't matter. A game world could easily incorporate some other group of attacks as "Killing", and the mechanics would lead to NPC perceptions following after such a shift.
Specifically, the mechanics that let some defenses (resistant) apply to all attacks, and other defenses (normal) apply only against some attacks. Against the resistantly armored targets, all attacks are protected against to some degree; but, against the normally armored targets, some attacks go right through, and this will be noticed by characters in the game world, leading to a conscious perception of the difference between Killing and Normal attacks (as well as an awareness of which defenses are "better"). The mechanics, as they are, cause this separation to naturally evolve in the game world.