If im right, he was bomber-hunting a lot.
This.
It's almost a prime example of how much impact flying style has on score.
Take a look at what I was flying and what I did kill. Almost all kills in fighter mode were the result of climbing to 15k and simply diving on 10k (or lower) bombers in 190D, then extending from the escorts (if any). That's all.
My K/D won't stay that high, it would have been much lower already if I had time to fly as much as I used to, only 10 fighter sorties so far.