So I just finished the game and it turns out that I've killed 1 person in the whole playthrough. I'm sure that I didn't kill anyone up to The Sorrow - the boss battle confirms this. I've replayed the rest of the game 3 times, but I always get this 1 kill result. I've tranq killed volgin (1st and 2nd time) and The Boss - gotten all the camos. For he motorcycle chase I've equipped the cold war camo and didn't fire even one shot (except maybe one time inside groznyj grad when it was required to proceed). No kills in the forest escape, sure of it. What am I doing wrong? Always this one kill...
Did you by any chance kill Ocelot to create a time paradox and press continue? If you did, it counts as a kill.
Other than that, I couldn't tell yah. I remember acquiring this trophy on my first playthrough. No one showed up during The Sorrow's river but I tranquilized plenty of guards during the chase scene (who all crashed and died as a result) but no kills were recorded.
Also, if you kill anyone before the river(even just your average guard) then die, choose continue, and proceed without killing that guard again then the guard will not be in the Sorrow's river, but you will have the kill counted against you.