None of what they've said would be subject to an NDA. An NDA will be used to stop them disclosing sensitive commercial and financial information they would be given access to during the process, before any transaction is completed or in the event that the takeover fails.
It really depends on what the NDA says. It's pretty common in M&A deals for the NDA to say the confidential information that can't be disclosed includes the substance and even the very fact of contact and discussion between the parties. There are a number reasons for that, including not scaring off your employees and not telegraphing business strategies to competitors. Having said that, though, those reasons aren't really that applicable here--everyone already knows the club is for sale and important employees are contractually tied down--so maybe MA doesn't care about the other side blabbing.
Seems fairly simple to me - the deal is all done and dusted pending PL approval which is just a formality. Negotiations have been completed, both sides have signed the paperwork, so that's it, the NDA is now defunct because everything is tied up awaiting regulator approval. At this stage an announcement is reasonable. The fact that the club officially confirmed BZG's first announcement is enough to suggest the announcement was agreed by both sides.
I'd even harbour a guess that the first BZG statement was something Ashley wanted because if he's sold the club and BZG remain completely silent whilst the PL do their fit and proper background checks (which might take time) each day that passes Ashley gets continued negative press coverage for not doing anything about Rafa's contract, not signing players, etc. Why bother with that if the club is effectively sold?
The one line I heard yesterday that causes a slight issue with all that is they said it won't be done before 30th June and it's down to Ashley to sort Rafas contract.
Sounds like it will rumble on all summer and be a perfect excuse for when Rafa leaves and we are scraping round the bargain bin in mid July again.