Deleted

The key is legit. It may or may not have been used. It's definitely not registered to your account.

It's the latter

It means that it's a key for that game, not if it still works. If the key was unused before you tested it and you already had the item, it won't become unusable. If the key was used when you tested it (giving the same message to download the game), it will still be unusable after your test.