Pretty sure an NDA can't prevent an individual from testifying truthfully in a court in the US no matter what the NDA says. So essentially the Police just lied.
If you're going to make a sweeping insult about all law enforcement in a given country at least try to use proper grammar when doing so. "Unpossible" is not a word.
It's also a meme, of which you may not be aware. It comes from Ralph Wiggum, the caricature of the special needs child on The Simpsons, when he says, "Me fail English? That's unpossible!"
In common use, it's generally taken to mean exactly what the GP poster intended: a mock expression of surprise at a thing that is, in fact, assumed to be the case.
There is a consistent trend in both prosecutors and police lying to defense attorneys and judges as part of criminal prosecutions in the US, across a large enough swath of the country and in federal courts (which inherently reflect on the country at large) to make it a fair accusation.
The choice of the word "unpossible" was precisely to mock the position that police lying would be surprising as unintelligent.
