@OMFG741I could be wrong if there is really a Bug like this happening.
But let me clear what i see there. 😉
You did 3 shots in the Clip, first shot was at a enemy that was laying on the ground and looked at you(which means that his Head and the Body lined up in a row).
So you might closely missed the Head and hit the shoulder and if he was already hit, you got the kill. Also the Killfeed on top right showed a normal Kill(not Headshot).
The other two shots are just hit markers, so probably no Headshots at all.
It might looked like Headshots cause you aimed pretty good for it, but there is always small Bullet drop. Also myself feeled sometimes like....that needed to be a Headshot....damn. 😉