''Its important to learn the darkslide first'' sounds strange to me, backroll handdrags have worked fine for me for quite some time, but a darkslide just doesn't work for me, I find a hand drag much easier..
I think he means this for the kite movement, which is the same for most surface tricks, like Darkslide, Jesus Walk etc.
But, this is an Inverted Backroll Hand Plant. A normal version of this trick is not inverted, you basically just lift your legs and your hand slides along.
The inverted version is very stylish as shown by Steven