Aatrox is hard enough to play as it is.

everyone keep mention this champ named Aatrox but i never heard of him or seen him? am i being trolled ?

It looks like Xin hit his knock-up while Matrox was diving him (i.e. the attack animation was started and while it got interrupted due to the knock-up it still went off) resulting in the double knock-up. I.e. it wasn't an Aatrox self-knock-up as it first appears. Not sure if Aatrox knock-up should have interrupted Xin's, but it really doesn't have much to do with Aatrox there (e.g. I'd imagine it would knock-up a Quinn vault which would leave Quinn stuck on top of Xin - since it's the same sort of mechanic - just like how Singed can throw Quinn during her vault even though her knock back was supposed to deny that I thought).