Seems reasonable to assume that a government saying "it wasn't us" or "it was them" is a heavily politically-motivated statement, not a strictly technical one. Regardless of it being accurate or not - there are reasons to keep quiet even if there's conclusive proof.

This is a case of a third party saying "we think it was probably X". You can't rule out other motivations here either, but there's a fair bit more room for it to be less politically motivated.