I think it's completely plausible that he doesn't get enough time programming and he's leaving because of it. Simple is growing. At this stage, he's a manager, not a programmer. Sounds like he isn't too interested in managing.
Most people seem to leave their respective companies and hang on as advisors. Maybe it's just too awkward?
I don't have to speculate about that or wonder if there's "awkwardness" behind it. Alex said so. Just read the post.
You wonder whether people write posts like this because they anticipate speculation about why they're leaving or how the company is doing. Of course, there's no win to be had in being honest and direct, because people are just going to invent their own stories. The narrative that eventually sticks is the one that is most fun to bounce around, or has the most resonance to people, or is most congenial to people's ideology.