Signing an NDA to talk about an unreleased product is not predatory, it's standard practice for virtually any business (especially the kind inviting random people off the internet to see them). Many jobs require you to sign NDAs just to go through the interview process.

There is nothing gained by not going to the meeting with Meta, if they want to launch their Twitter clone they are more than capable of doing that regardless of whether or not this guy takes a meeting to hear them out. All he's done is learned less about what they plan on doing leaving him less capable of taking the best course of action, and if you trust him to make the right decision then that's objectively a bad thing.