Quinn bug on ARAM

So i was playing ARAM as Amumu and the enemy team , who had a Quinn on it, killed my team as i tried to run back to my base Quinn came in on her ult to kill me so i threw a snowball at her to knock her off her ult but when it hit it did nothing and she killed me and won the game off it, so i looked at her champ page and it says and i quote

Taking champion or turret damage puts Behind Enemy Lines on a 3 second cooldown.

Unless summ dont count as champion dmg ,which if they dont i think is not right, it should have knocked her off