Does flinch work properly?

[MetalBush 0]

I would really like for someone to explain to me how the flinch mechanic is supposed to work, unless it's random, because...

 

Shotguns often flinch you. I've experienced this many times. But just minutes ago I engaged in combat with a player running perpendicular to me, roughly 5 meters away. I send shots at him of which a couple hit the body. I know this because of the blood hitmarkers.

He then stops running, turns to me, shoots me with his Thompson and makes me flinch.

 

He proceeds to kill me and I wonder why I'm the one flinching and not him? All this happened in mere seconds but I'm certain MY shots hit first but HE made me flinch.

Is there a mechanic behind this phenomenon or is it based on randomness?