My guess would be that it is using your local database (as it can’t access OSMs database directly), but the map shown uses the tiles from tile.osm.org which obviously show the data in the main osm database. If you open Potlatch, or user the Databrowser, you should see the data in your local database.
If you do want to see map tiles showing your local database content, you will need to set up a tile server in addition to the Rails_port server. Have a look at Mapnik / mod_tile / renderd on the wiki for some ideas of how to set up the rendering part.
The datasource is defined in inc/datasource-settings.xml.inc. You either create that by hand by copying the .template version and adjusting the fields for your environment, or by running the generate_xml.py script with those settings.
You then point renderd to the osm.xml file.
The rails_port is not needed for a mapnik/mod_tile setup.
Thank you very much Ldp ! this is a great step forward for me
So I guess that if datasource-settings.xml.inc doesn’t exist, there is a default setting somewhere ?