Fiora parry bug?

I found out that her W, parry; could block out Gnars auto attack passive 3rd mark magic & the auto damage with it. is this some bug or something? I cant see how this is remotely fair if not. Isn't that the point of him bulling other top laners like her? I feel like this is like something of players abusing the passive when it's proc worked for range champions.

Even got a link showing it in a pro play around the 4 minute mark, 6:07 & 6:40, 11:08

I hope this is looked into because Gnar is struggling enough as it is lately. His early game is very weak & late game play is not all around possible lately with the new season changes making games much shorter.