ok guys ive just finishing rewatching a couple of episodes of the firt part of naruto and while kakashi was training naruto,sakura,sasuke he states to sakura to kill sasuke and it was just a test to give them a glimpse of what to expect in the shinobi world. so my theory is he went through the same experience. referring to the same situation he had with rin. its just a little brain storm that came up after watching that episode.