You can run the Audit3dm command on the file, it will give you detailed info. At the end, you see the plug-in data and how much memory it takes up. In this case it seems to be a “mystery plug-in” with no name, just an ID…
Model User Data Table:
user table[0]: (2083 bytes)
Plug-in id: 06F3218E-F5EC-4f6c-B74C-14583F0ED7BC
user table[1]: (28736 bytes)
Plug-in name: Renderer Development Kit
Plug-in id: 16592D58-4A2F-401d-BF5E-3B87741C1B1B
user table[2]: (28 bytes)
Plug-in name: RPC
Plug-in id: 1F908FF5-4984-45a6-95F0-A81CE979A4D7
user table[3]: (497 bytes)
Plug-in name: Rhino Render
Plug-in id: 5DC0192D-73DC-44f5-9141-8E72542E792D
user table[4]: (12399013 bytes)
Plug-in name: V-Ray for Rhino
Plug-in id: E8CFE179-B60C-411a-8416-62A893334519
user table[5]: (29493 bytes)
Plug-in id: 491AC9CC-69C8-4369-AB68-019A44F49DDC
6 user tables, 12460456 bytes (offset 25078 to 12485534)
Archive size = 12485554 bytes (end mark size = 12485554)
Maybe this thread has more info… --Mitch