Three questions..
Isn't stream sniping a banbable offense?
If he thought it was stream sniping he's fine with reporting it, do they ban without evidence?
Did he report it and did the person get banned?
Important questions. The thing is, stream sniping, especially on Twitch, is absolutely forbidden. If he thinks or has a massive hunch someone is doing it, he absolutely should be reporting them. Generally, stream sniping is a tough thing to ever fully confirm, but Twitch does do mini investigations and reviews gameplay and chat, etc, to try and sort it out. I've been stream snipped before and I mostly let it go, but it is a pretty cruddy thing to do to gain competitive advantages.
I mean, is this really something people are mad at him about? People can keep saying someone didn't stream snipe, but unless they are in the room with the person it's not like they actually know. Stream sniping is typically most noticeable when someone beelines directly to your location ready to kill when there is no way they could know your there.
I don't think him being concerned someone was cheating, or convinced they were, really means much.