"All Cops Are Bastards" doesn't preclude that cops are incapable of performing any good action - it's meant to portray the fact that cops serve the interests of capital (not the people they contend to "serve and protect") and that the systems of policing vehemently oppose any effort to change that fact (don't take it from me, ask a former bastard cop).

And even in this instance it is much more likely that if the Portland PD didn't have a non-intervention policy, they would spend their time tacitly supporting the Proud Boys against the anti-fascists considering that is what they've done at every opportunity up until this point.