When you're on the streets with the protests, it feels extremely primeval. The micro-scale interactions of the protest movement is like looking into a microscope at microorganisms, blobs of life that just kind of move around and sometimes eat others but most of the time just float there.
It's a decentralized, rather polite mob. Angry, yes. Scary, sometimes. But otherwise, just a lot of yelling, a lot of "tactics" - like retreat, advance, wall off here, go here, go there, run. It feels like there's no real goal or direction of the protest except to exist, and I think the author captures that feeling very, very well.
The police also have that same feeling on a micro-level, not much thought or control, just an instinctual reaction or set of rules to follow.
One party existing to express concerns and vent anger. The other party existing to restrain and disperse.
Of course, on the real level, the two parties have deeply rooted goals and feelings. The police want the protestors to stop protesting. The political party wants the people to be absorbed into China. And the protestors want to preserve the unique individuality of HK and to allow it to grow and thrive.