Ashe Ult VS. Tryn

I was in a game today, and top was losing drastically to a Tryn. He pushed to second tower, so I went top as Ashe. I had my Ult, and used it. To my surprise, nothing happened. The ult launched, it hit, but Tryn wasn't slowed, stunned, nor did he have any items that would negate it. He didn't even Have anything by the end of the game. His teammate accused him of hacking. I think it may be a bug...either or, just bringin it up.