The perception of the guy being shot down is always biased, my own included.
There are a couple of things that can occur that would look like the guy had rockets on his ride.
Figure the merge, if everyone is 350-450mph then you have closure at 700-900mph. Network lag really becomes obvious. A lot can happen at these speeds over 150msec (300msec counting his and yours). This is where the timing thing happens. A lot of folks start pulling up (vertical turn) right at the merge, sometimes you catch them starting early if they misjudge the e-state. Gives you a good cold side shot if they do. If their timing is good they are halfway through the turn at the time you pass them. If they managed the vertical move well, they won't loose much velocity but they will gain enough altitude that an unloaded dive will allow them to match the speed.
Another thing is avoiding the head-on. I see a lot of folks giving away position to avoid this. I mean radically avoiding, providing a lot of vertical or horizontal seperation. Ideally, you don't want to have more than 1/4 of the turn radius for seperation and less is better. You really don't want to be shot in the face with a handful of 20mm either. I usually try to pass under and to the side, just under a wing. Its hard to push negative and make a shot. The only times I've been hit doing this is by misjudging the bog's e-state, he's usually slower than I thought when he gets hits on this move.
It's hard to say what happened without being there in the cockpit, I will say that 400+ is a little slow with less than 6K AGL n a P51.
IMHO,
