With JomSocial 3.1 onwards, the dashboard counters are implemented in JomSocial Backend Panel. These counters hold various statistical data about your community and are available to all admins in main control panel view.
Is members counter wrong?
No! By design members counter will only show those users that have at least one (1) JomSocial User Point
User points are assigned on every individual action available in JomSocial and it is the easy way to recognise how many users actually used your community.
Hacking the code to show all members on the site
If you still however want to show all users that have ever registered on your entire Joomla site modification is quite simple
Just open this file JOOMLA/administrator/components/com_community/views/community/view.html.php and on (or around) line 41 find this code
The important bit here is jomsocial parameter. Change it to all so that it becomes
Now you will have all members counted even if they never opened JomSocial at your site