Look, I'm not going to call Jay a cheater. I have never played with him. I have no idea what he does in a typical game except apparently shoot a lot of heads. He could just be doing this kind of thing in Private matches and then quitting so he gets no credits out of it, because he's just that goddamn saintly.
What I do know, absolutely, without doubt, is that this video was made with some sort of aim assist going on.
And I'm not mad about it. Because as I said, I've never played with him and I have no confirmation he's cheating when playing with others. If anything, I find this video hilarious. It was blatantly obvious from the first 20 seconds that this was the work of aim assist, and funnier still that there are people who would claim otherwise.
I do not care how skilled you are. You do not have perfect head tracking 100% of the time while your target is cartwheeling in the air or flinching from a shot. Take a look at 2:06, the two shots on the Nemesis. He shoots a crouching Nemesis, then he perfectly tracks her head WHILE SHE'S FLINCHING. That's not prediction. That's real time head tracking through a very rapid animation. That isn't human.
I do not care how skilled you are. You do not snap to the head of a moving target from another moving target on a high recoil gun, without any pause and using razor straight-line, incredibly rapid mouse movement that never undershots or overshots its target. I want you all to do an experiment for me. Open up MSPaint and, using your mouse and Pencil Tool, try to rapidly draw a straight line that stops at an intended point. Marvel at how you fail spectacularly. Now try it immediately after jerking your mouse upward to simulate recoil. Yeah. Humans don't move their mouse in perfectly straight lines of precise length like that. Ever. Not ever.
In contrast, take a look at d_nought's Apply Directly to Forehead video
here. Notice the irregular mouse movement when switching targets. Notice how he sometimes overshoots the movement and has to compensate to get back on target. Notice how he's predicting target movement rather than keeping the cursor perfectly tracking the target's head the entire time. If he's using any artificial assistance, then it's a damn refined one.