"The conclusion drawn seems like the most realistic explanation."
I'm not sure I agree. I imagine either of us could find evidence of police corruption, institutional racism, or myriad other issues. There are a lot of police in the world.
I'm not excusing racist or crooked police, I'm suggesting that there could be multiple explanations for the drop in complaints.
"Your alternatives don't seem credible considering the change also occurred when police weren't wearing cameras."
And that would seem to indicate that on average, the officer's in question were behaving better, and I expect that's the case. It could also mean that the public was aware of the cameras too, and that word gets around, which is likely in smaller communities.
If I had to guess, I would guess it's the former. But I'm not a police officer, an ombudsman, or a victim of police abuse, so I would be speaking from zero experience.
There's also a long catalogue of evidence that white people as a group have been institutionally racist.
Your own race (just as an example) is none of my business, and obviously I sincerely hope you're not racist (which I very much doubt you are), but in any case I'm in no rush to jump to conclusions about either, which is kind of my point.
Presumption of innocence exists for more reasons than just protecting citizens from the state (although that's an important one). It's because our gut instincts are most unscientific judges of character.
I will say that I'm glad they've found a strategy that seems to have such a strong positive impact on police-public relations, though.