When you restarted Opus, did youfully exit Opus (via File / Exit Directory Opus), or just close the window and open a new one?
If the drive is still showing up after a full restart then Windows must be reporting it to Opus in some way, but if it's only after closing & re-opening the window then it could be some incorrectly cached data.
Please also try turning off Preferences / Folders / Virtual Folders / Native display of 'Computer' and then going to My Computer in the file display (it won't affect the folder tree, so ignore what that shows for this test). Does the drive still show up then?