He is correct. What trips you up is that you have a Gen 1 HDS7. If you replaced that unit with a Gen 2 or later at some point, the map data on a card would be shared for the two units via their Ethernet connection. Your LSS1 box has an Ethernet switch integrated into it.
On a related note: Your system units will share GPS waypoints as it stands. If you add a waypoint to one unit, it will be visible on both. If you delete a waypoint from a unit, the network and other unit should be powered up (because waypoints are stored on both units). If you delete a waypoint with the other unit turned off, the waypoint will reappear when the other unit is turned on. The "reappearing waypoint" issue has tripped up many an owner.....lol