I've installed the forum and map modules at my test environment and establish that the map module do not show the forum members as described in the documentation. I see the map but without any markers.
So I have visited the demo version directly at silverstripe.
I registered a new member at the forum and compared all registered forum members with the showed information on the map.
My opinion is that the markers (location and quantity) on the map are wrong and I have no idea how this come about.
Have a look to the attached files.
7 registered members vs. 4 map markers
5 NZ, 1 CH, 1 DE member vs. distributed markers all over the world