Minor Sion E Bug

I noticed in a game yesterday, April 18th 2016, while playing as Sion, I hit an enemy minion into an enemy champ with my E, Roar of the Slayer, and an ally proceeded to kill them about 1.5 seconds later, and I didn't get an assist for it. The minion bowling ball does a bit of damage and slows the champion or any other enemy minions it comes into contact with, so I would think doing minimal damage and slowing an enemy champ would grant you an assist. And yes I am positive I hit them, I was using the Mecha Zero Sion skin, which when bowling, it puts a blue circle around minions and champions when they are hit, which I clearly saw. Please look into this, I'd like to get credit in games where credit is due.