I wouldn't make anything of it. What the DA is saying (and there is no way to find out if he follows through) is that separate grand juries will be used to investigate possible crimes by bikers, and possible crimes by police on-scene.
My sense is that he is putting on a show to create the impression his actions are balanced and reasonable.
He can put both types of cases before the same grand jury, if he wants.
“My sense is that he is putting on a show to create the impression his actions are balanced and reasonable.”
Not everything is a conspiracy.