[GAMEPLAY] Zilean ultimate not working on Warwick?

Hello,

During one of my matches tonight I experienced what I thought was me being out of range for my ultimate as zilean. Upon further review of the video I've attached, my ultimate went on cooldown and you can clearly see the animation on Warwick until he dies. It looks as though it occured while he was CC chained (Sejuani ultimate into thresh hook). While this didn't end up in us losing the game, I'm curious as to how it happened.

Thanks.

Phin