It just ("just") sounds like he's out of alignment with the kernel development process.
That shouldn't be too surprising - I mean, its an old project with a whole lot of technical baggage. Projects tend to slow down over time. And that is legitimately really frustrating when you want to shake things up or push for change. I would be rubbish as a linux kernel developer. I have the wrong temperament for it.
There's a reason why some tech companies interview for both technical skill and culture fit. Sounds like he's got the technical chops, but he's not a good fit for linux.
And when you're in a situation like that, your choices are essentially Voice or Exit. Voice is to do what he's tried to do - kick up a fuss about the problems to try and get them fixed. Thats a skill on its own - and it sounds like he's not been super effective at that. The other option is Exit. Which of course - sensibly, he's now done.
> he has gotta Stop Posting and keep those kinds of thoughts away from his keyboard.
Nah. Bottling this stuff up is a bad long term play. You end up getting bitter, cynical and resentful. I think we've all worked with people like that, and its miserable - both for the person and for their coworkers. I think its better to shoot your shot. Even if you miss - as he has here - you learn a lot about yourself and the world. And there's no shortage of interesting projects out there to work on. Pick something that matches your speed.