It appears that 4+ days ago, the airport police in Paris planted explosives in an unsuspecting passenger's bag. They didn't make a note of who the bag belonged to or where it was going, because they thought it'd be caught by their systems. It wasn't, and they lost track of the bag and its contents.
Now, they "hope the person who finds this will take it to the local authorities." Oops!
Official sources have indicated that the police will not be using real explosives in future tests.