[Gameplay] Ornn Passive proc cancels Galio W

I faced off against an Ornn top as Galio today and noticed that Ornn is able to cancel Galio's W with the auto attack passive proc that he gets. As far as I'm aware this shouldn't happen as Galio W specifically says it can not be interrupted by Crowd Control. It happened any time that I tried to channel the W while I had the brittle debuff on which I tried several times during that game to make sure it was what was cancelling the W.