[GAMEPLAY] Warwick ult persists through Gnar ult and Sivir Spellshield

I was playing Gnar in ranked solo que with a Sivir on my team. During our last teamfight, the enemy Warwick overextends trying to catch Sivir, I use my ult to throw Warwick into a jungle wall (I believe this is before he ulted, but I am unsure). Immediately after I ulted the Warwick, I realized he somehow landed his ult on Sivir (Sivir states that she used spellshield, which I am unsure of, as I did not see it) and I finally stopped his ult with my W.

The series of events should go something like this:

1. Warwick gets ulted into a jungle wall by Gnar
2. Sivir (supposedly) Spellshields.
3. Warwick ults Sivir while he should be stunned.

This all happens in quick succession.

Visually it looked like Warwick started his ult mid flight during my Gnar ult, but without teleporting to Sivir.