(a judge can, obviously, treat this situation exactly as an NDA, but they can choose to not do so as well).
The difference is the effort on the part of the plaintiff. A formal, signed, NDA is very difficult to challenge. An email agreement is easier to challenge, but a properly formed chain can be just as strong in the end, though there are extra steps in the process.. taking weeks to iron out. A verbal contract where rely on what the parties each believed they had as an agreement and what the judge believes.
I've had some experience with lawsuits