Ekko able to ignore knockback from Lee Sin's Ult?

I was playing Lee Sin during this game and when I ulted Ekko during his E, He just stood still and did not receive a knock-back. As you can see in the skill bar on the bottom on the video, my ult did go off but it did not give Ekko a knock-back. [zombie-brand-mindblown] I do not know if knock-back is negated from any other champions abilities though.