So, recently some fediverse admins (mostly Mastodon) and the founder of Mastodon, Eugen Rochko (Gargron), where contacted by Meta/Facebook for an NDA meeting. We know nothing about it, but we're pretty sure that it was about this project92 thing that Meta/Facebook is creating to "compete" with Twitter.
So a lot of Mastodon admins already singed a pact to immediately block any Meta/Facebook activity in the fediverse as soon as it comes up. My Mastodon instance, fosstodon.org hasn't singed that pact and I'm pretty worried.
The following image is an screenshot of Gargron and dansup (creator of Pixelfed) talking about this. These posts were deleted, even from the wayback machine.
I agree, only crackpots who are afraid of having their unoriginal ideas stolen ask for an NDA for a meeting.
The only thing I can think of is that META is afraid of people finding out how desperately they are trying to stay relevant.
The other reason as someone else pointed out that might be going on at the meeting is a $ amount for a contract of some sort. Companies often want to such business agreements confidential, especially the $ amounts.