I don't think those were stun grenades. I think they were tear gas canisters that emit a startling bang when they are deployed. But they are not bright or loud enough to incapacitate the way a stun grenade does.
Not to say that means you should support the use of this type of tear gas canister, of course. It's just a different critter.
I dont support OWS, but the police are no better.
Both are exploiting this situation for gain.
Watch the new toys these cops get next year as a result of this.