A lot of people don't trust or respect the Anon branding. My personal view is indifferent but I do admire some of their work. Although there is a lot of uneducated and ignorant people waving that mask around even if it is with the best intentions. Using official Anon branding may backfire, but it could also pay off if you get a lot of their hardcore supporters onboard with this project. I've mentioned Anoncoin to a few of my hardcore crypto friends for a good while now and some of them are really put off by the fact that Anoncoin uses the official Anon branding.
Maybe that was a screwup, and maybe they chose a person who had never even served on that department in order to force the hand of the local Sheriff.... just saying.
Each person who uses the Anonymous symbol does so on their own. They don't speak for anyone else. The name released on that twitter by the same one(s) who released audio was bryan willman. The actual officer involved was darren wilson.
Apparently a fake facebook page was set up by the police dept to draw away people looking for that officer. A photograph of the officer who shot the person was available hours after the shooting, and was seen by those who leaked that name.