I am a bit surprised how flexibly OpenCities Map both in GUI and documentation jumps between PostgreSQL and PostGIS. Sometimes my feeling is that authors and developers are not sure what is what and whether PostgreSQL is mandatory or also PostGIS is required and why and when.
I am sorry I am stickler for proper naming and terminology, but to use PostgreSQL in requirements and PostGIS in a description of spatial databases is not correct. Moreover, nothing like "PostGIS Spatial" exists!
The database is PostgreSQL, so the connection and spatial source should always be PostgreSQL, not PostGIS.
PostGIS is (only) spatial extension of PostgrSQL and it's more like application layer on top of DB engine.
It also would be nice to add a description what from PostGIS functionality is used by OCM, because PostgrSQL itself supports some geometry types.
P.S. Not exactly the same, but I guess nobody will dispute that it's not correct to use MicroStation instead of MicroStation PowerDraft. Mixing PostgreSQL and PostGIS can lead to a same level of confusion.