Okay, so I reviewed the video in HD and in slow motion multiple times, and it appears that you missed your first 3 shots, shot the Sova 3 times, and the last shot didn't register because you died before the bullet had reached him, so it probably despawned with you. You should have gotten 3 shots, I think 2 on the body and 1 on the legs (maybe-it was right in the middle), and I don't know why only 2 shots got registered by the game. This IS weird!
Edit: I think I figured it out while playing some Deathmatch. So sometimes when I'm spraying and I have my crosshair on the enemy, my shots still don't connect because of the random spray pattern and the shots not always landing where your crosshair is. So maybe try not to spray as much, and see if that helps.
