Yeah, it can be a bit confusing. The LAPP appliance is optimized to be used as a web server, with PostgreSQL as the database back-end listening on localhost.
OTOH, the PostgreSQL appliance is configured to be used as a standalone database. The database is not bound to localhost so you can interface with it over the network.
Configurations optimized for different usage scenarios
OTOH, the PostgreSQL appliance is configured to be used as a standalone database. The database is not bound to localhost so you can interface with it over the network.
Does that make sense?