Wow dude I thought I suck lol, jk it's probably lag , yesterday day I emptied a whole vex magazine into a guy and it didn't even break his shield and his health regenerated right away
If I had to guess id say it's an extreame case of lag, and that player wasn't in the position you were shooting anymore. Hence when you died they were to the left of you.
I've seen this happen way to many times to count and hope that server lag like this can be addressed. I've personally shot 3 golden gun rounds into a person only to have them kill me then die a minute later.