Illaoi E activates after Kayn R [Gameplay]

Last game I played there was an Illaoi on the opposite team and I was playing Kayn. Every time Illaoi R'd me and I R'd inside of her, upon exiting with my R her slow on her E would proc. She never landed or even used E, but the slow on her E would trigger on me after exiting her if she had ulted me beforehand.