Or maybe, that which didn't bring you to below 50% didn't do meat point damage. This is from looking at certain effects in the game where essentially the bloodied condition was used but not mentioned. Things like the champion's regeneration which only works if you're below 50%, or the life cleric's channel which could only bring people up to 50% for some reason (cure wounds can restore above 50%, not sure why life cleric's ability was held back). I think I spotted more, but these two stand out.
Note that I don't really care how people describe hit points, your killing blow is as good a description as any, but for me, I did like the idea of 50% being bloodied and starting to take actual physical damage, even if it was just a game mechanic trigger.