Ok, I think I get it.
Kusuru and Hideo's chase represents their control over the zombies. Kusuru is the one directing all regular zombies to attack people. Recall how he was there amongst the horde that bit Ezaki. This is why, when Hideo turns to fight Kusuru, we see him turning to fight the zombie (which he had previously ordered to kill each other).
People are acting like this is all being made up on the spot, but the idea of the zombies being a hivemind has been set up since they first started appearing. Only thing I still have no idea about is where the heck that mutated zombie came from and why it seemed to know to save Hideo.