You're right, but I don't think they would make this accusation purely due to a mistake. In my opinion, there are 2 possibilities: 1. The FBI knows who did it

You're right, but I don't think they would make this accusation purely due to a mistake. In my opinion, there are 2 possibilities: 1. The FBI knows who did it and is telling the truth by saying it's North Korea. 2. The FBI knows who did it and is lying by saying it's North Korea. Personally I think they're telling the truth in this particular case.