I can’t say for sure if that happened, but if they made a clear promise and then did something else, it’s perfectly reasonable to call that out.
I don't think it's easy, there's inherently some interface(s!) where it's a hand-wavey 'get the thing from the private bit', and defining that sensibly is hard, and if you try to do it well will probably lead to a lot of meetings, scope creep, etc. - and as far as that goes it's not easy anyway, since it's highly technical and implementation-specific yet also a management/policy decision to make.
Why be transparent (or try to appear transparent)? To convince people to trust your platform (or to recruit - which seems to be another goal of the post). Why would Twitter want or need to do this now? Well, there is a bit of context. This disclosure doesn't exist in a vacuum.
If your play was "it's some source code, hence people will think we are open, and that should be really good for us", that would make you a very special kind of idiot in this space.
