My guess would be that the Google head honcho on-site asked nicely and offered some sort of carrot (e.g. "we will tell you our other spooky floating facility pl

My guess would be that the Google head honcho on-site asked nicely and offered some sort of carrot (e.g. "we will tell you our other spooky floating facility plans in advance"), and that the Coast Guard employee was "required" to sign the NDA by a boss who liked the deal.