As far as the actual legality of the things he does, it seems like pretty much everything in the talk I had heard before, mostly through the Snowden files.
All of this under the banner of state secrets justifying these actions. Whereas in any corporation or visible branch of government the waste would have been a scandal. In the NSA the use of state secrets means power concentrates and individual employees have little recourse (Snowden, etc.).
This is what I'm countering, perhaps something like this needs to be discussed as it's in the public interest.
Of course whether those slides would cause 'serious damage' to national security is a whole other matter or maybe it was 'authorized'.
Classified information does not become unclassified just because it is publicly available if I remember correctly. Either way, I can't comment on whether including them in his slides is disclosing/divulging or not.
Yes, at least in this talk he's very careful only to disclose what can be inferred from already public information (e.g. Snowden leaks). People from his former line of work are kind of used to this, I guess, as they probably cannot even discuss every detail of what they're doing with all of their own colleagues during lunch breaks.