[GAMEPLAY] Fiddlesticks crowstorm channel not being interrupted

In playing an ARAM game tonight as Aurelion Sol, near the very end of it, Fiddlesticks started to channel. I hit him with Aurelion's ult, his ult went off without a hitch.

Reproduce: Level 6+ Aurelion Level 6+ Fiddlesticks Start Fiddlesticks Ult Interrupt with Aurelion's Ult

Link: (newbie, no idea how to record a game / video, etc.) here is the match history URL http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/2182917068/230864629/eog