To quote Vinnie Dorion:
I learned this trick by starting with a flair then adding a grab, I basically mixed a grabbing flair and a backflip with a Liu Kang grab – et voilà, an underflip.
Sounds like he's saying it's the same trick, eh?
BTW, the way you landed (overrotated the flip), is how Iannick B. broke his two arms a couple of years ago. Stick to the soft stuff for now.