Guests can add a movie if POST BEFORE REGISTERING is enabled but it will be hidden until the member register then the name provided in registration process will show up, not guests.
I can imagine two things here. 1: the user who submitted the movie were deleted then the content, if not deleted, will be authored by a Guest (there’s a Core setting for this). 2: the widget should be showing wrongly the author.
Even if it’s a bug, will be fized in next version (1.0.3) as it isn’t crashing your board. 1.0.2 is pending on marketplace for a few days now so it needs to go live first.
I don’t think people will want 10 times the same movie showing up so to prevent duplicates, you can’t add an existing movie. If you deleted it, it still exists and shows in Moderator CP -> Deleted Content for 30 days (default Core setting value). Delete it from there and you will be able to add a again.