|That is correct. |
Once you have the file opened, you should be able to go to the Shapes Sidebar, then select More Shapes. From the pop-out list, select the Network heading and Detailed Network Diagram should be one of the selections.
If it is not appearing in the list, I would recommend a repairing the Visio installation as those are built in shapes files that are installed with Visio by default.
IT Desktop & Network Consultant - MOS Master Certified, MCP, MCSA, MCITP - Windows 7, CCNA Certificate Pending, A+, Network +