What we MIGHT perceive as citizens doesn't mean the police don't follow their own law.
If, for example, the individuals cited were approached by the police and weren't under arrest at the time things happened, then it's reasonable to think self-defence has been enacted if the attacker think a n officer is abusing his brother 'for no reason' (not cautioned at the time).
Context matters and I suspect the officers own cams captures the context and why the jury found 'self-defence' a legitimate case.
Some of you need to think in terms of the law and evidence, not as angry citizens.