That probably doesn't matter to the people pushing the NDA. Why should they care about the realities of contract law, when they can just make up lies and get people to believe them under threat of lawsuit?
It's just like how so many car dealerships will tell you that getting your car serviced anywhere else will "void your warranty" even though that's blatantly illegal.
It's just like how so many car dealerships will tell you that getting your car serviced anywhere else will "void your warranty" even though that's blatantly illegal.