All the other cultural issues he seems to bemoaning are all consequences of growth in a startup. Information flow gets harder with more people.
As far as the CMO moving on to github, that certainly doesn't seem to be all that sinister of an indictment. If you have experience in marketing a developer tool to developers and software businesses, you're probably going to leverage that experience getting a job marketing a developer tool to developers and software businesses.
The one thing he's likely right about is that there probably isnt enough market to actually chase, github has a huge piece of it already and hasn't been able to liquidate, so its not obvious where their growth is going to come from besides eating away githubs marketshare. But thats probably why they seem to be pivoting more towards a holistic tool set that is bigger than version control (like the atlassian example). But only time, execution, and a whole lot of luck with show how it all pans out.