How does architecture actually reflect this.
A colony of ants couldn't create Greenwich Village. Neither could a tribe of hunter-gatherers. There are underlying levels of infrastructure -- some of which require planning -- in order to enable the higher-level decentralized behavior.
Well, a colony of termites certainly can create cooling systems in their mounds, so I don't see why decentralized dumb units can't create requisite infrastructure. ChristopherAlexander suggests an individualistic alternative to sewage systems. (See also SepticTanks) You can think of equivalents to other centralized systems and services.
The termites has evolved to create the cooling system. They are programmed to do it by millions of years of evolution. It doesn't work that way in humans, because our cities just don't exist long enough. Advanced infrastructure may be added in a patchwork manner on top of existing developments or it must be planned beforehand. It can't just emerge from actions of many dumb human individuals.
It's true that a decentralized process is unlikely to construct the same infrastructure systems we currently have beneath our cities. But that doesn't mean they couldn't build equivalents under equivalent cities.