At Google, generally available means it's no longer in testing. It's a development lifecycle term.
;-)
They know the majority of their users are going to think 'generally available' is exactly what it sounds like, not their made up meaning.
The Google announcement is pretty direct about the plans the feature is included with, and how to enable it.
Bit of both, maybe.
Internally GA means released to at least some end users without caveats like "in beta".
Marketing are just repeating that. Maybe they are being deliberately disingenuous, or maybe they are just parroting a phrase they don't understand.