Hi,
Unlike iMovie 9, iMovie 10 projects are not files. Rather they are folders in the iMovie library that contain the project data that gets assembled into a project when you click on the project's icon from within iMovie. iMovie links to the iMovie Library folder to access the project data. It looks like you have moved the project data folders from the library package contents folder that displays when you control click on the iMovie Library folder contained in the Movies folder. If that's correct, you have broken the link between the project data folders and the iMovie app. If you can copy the project data folders back into the original library perhaps you can restore the link. I don't know. You must never move or change anything in the iMovie Library package contents. If you do that you run the risk of corrupting the library.
Another thing you can try is to go to your iMovie Backups folder that contains periodic backups of the iMovie library on different dates. The file path is: Go/Home/Library/Containers/com.apple.iMovieApp/Data/Library/Caches/iMovie Backups. When you get there, you will see a list of previously backed up libraries by date. Click on the library dated immediately before you moved your project data folders. iMovie will open in that library and hopefully your projects will still be intact. Not sure that it will work since you have removed the project data. But it's worth a try.
If you have a Time Machine or other backup, you could restore your iMovie library from there and you projects would be intact.
Projects must always be contained within an iMovie library. If you want to move the project you either move the whole library or you copy the project to a new library from within iMovie (NOT from the package contents), and then move the new library that contains the project. iMovie libraries must be contained on drives that are formatted Mac OS Extended (Journaled). Do a control-click on the external drive's icon to see its format. If it is FAT 32, a PC format, you can reformat to Mac OS Extended (Journaled) with the Disk Utilities app located in the Utilities folder in your apps folder. However, reformatting the drive will erase all data on it, so you first have to remove or back up elsewhere any data that you want to save.
Hope this helps.
-- Rich