staiger, if you imagine a forehand net kill for a right handed player, you will be likely holding a panhandle grip (similar to a tennis forehand grip - called the semi-western grip - random fact

). Imagine you hold your arm directly out in front of you, and the racket head is pointing upwards. This is 12 oclock. rotating to the right 90 degrees would get you to 3 oclock, and the other direction is 9 oclock.
A brush net kill is normally played by "brushing" the shuttle, by moving the racket head from 3 oclock anticlockwise to 9 oclock, with a contact with the shuttle at roughly 12 oclock. This would make the shuttle travel directly forwards, or downwards and forwards if you angle the racket face to point downwards slightly (I believe there is an excellent brush net kill video on badminton bible...).
This brushing motion is very much a "sideways" brushing motion from right to left (There are a few more things that make the perfect "brush kill", as the path of the racket tends to arc forwards slightly instead of just sideways, but these are the basics) and is the same one used by most professional tennis players for top spin forehands when the ball is high (called a "windscreen wiper forehand" in tennis).
The variant that I see lee chong wei play (and many top professionals) is the same brushing motion from 3 oclock to 9 oclock, but where the shuttle is contacted at more like 2 oclock or 1 oclock. Thus, the shuttle is being brushed "upwards" rather than from right to left. I would refer to this as a top spin shot, because the intention is to hit with spin to make the shuttle dip afterwards.
I am interested to hear what you guys think. Do you think its "top spin"?