If he wasn't the owner, then I don't see how he would be able to remove the owner's privileges?
That would also not allow that user to permanently delete anything. The real owners should be able to restore the material to their original locations.
Or did each individual file lose their connection to the previous location when the folder too was deleted?
I mean, if you do a single manual file restoration by the rightful owner, will that file only end up in the root of said file owner's Drive?