In the Metaverse, the blade just passes right through, if you swing it quickly enough. Here in Reality, Hiro's expecting a powerful shock when his blade hits the New South African's neck, like when you hit a baseball the wrong way, but he hardly feels a thing. It just goes right through and almost swings around and buries itself in the wall. He must have gotten lucky and hit a gap between vertebrae. Hiro's training comes back to him, oddly. He forgot to squeeze it off, forgot to stop the blade himself, and that's bad form.