Yeah, it's not the event or the video that makes me think there might be a public reaction. Because there are stories like that almost every day, and most don't result in anything.
But for whatever reason, this one seems to have gone quickly viral, and I was seeing many calls for action as soon as the news broke. And you've also got memetic iconography going on, with the unknown victim being labeled "Africa" and such. People latch on to things like that. That's what you need to look for. The incidents that get noticed, and trigger that action button in people. And no, it doesn't really make sense why some do and others don't.
Like in Ferguson... that story didn't get widespread attention at first, but I saw a little bit of buzz immediately after it happened. And the handful of news articles published within hours of the event all described how citizens immediately poured out of surrounding buildings and formed an angry mob. When I read this, I could see that this incident wasn't going to be allowed to pass quietly. I posted on Bay12 that day "there's going to be a riot here tomorrow". And there was. And THEN the story got national attention. Why did it happen like this, when we've learned since that this was a community that had been quietly enduring oppression by a corrupt and violent police force for many years? Who knows?
This LAPD incident may not result in anything. Response seems to be hot, but not blazing like Ferguson was. We'll see.