"Here is how the lock works, but you still can't unlock it without the key."
What I'm telling is that those who created the chipher in the first place have the reverse algorithm that doesn't require the private key to decrypt the message.
So the the guy who created it was smarter than the entire rest of the planet combined. As so smart that despite SHA-2 being the single most researched cipher by researchers and academics all over the world nobody else on the planet has discovered this "weakness" in more than a decade? Furthermore nobody has stolen, or leaked to the public this weakness either?
Highly unlikely but one can never prove it isn't true.
Still while we may not be able to prove it isn't true, you have no way of knowing it is, so claiming you know they know is just bullshit right?