That's how it goes. He was probably in a premade. He can say anything he wants because your 1 report won't get him banned. But if you say anything (and I do mean anything), you will get banned because their votes will trigger an automated review. It doesn't matter if you said 1 negative thing after he said 100 to you. YOU will be the one banned.
IDK why Riot feels the need to do this to people. They already have a mute button and curse filter.
Forethought: I think it's funny people are down-voting me. Are they down-voting because they think I'm wrong? I'm not wrong. Are they down-voting because they don't like the way it is? Because I'm not the one that created the system. Riot did. Down-voting me isn't going to change anything.