The points he makes speak from experience. It's a perspective that is too often ignored by younger generations: You can't always quit a job when the work gets boring -- sometimes you just have to push through the tedium if you want to be the best at what you do. This is a widely applicable bit of advice.
But the way this message is presented -- to chastise loren, the 20-something who quit AirBnB because he "got bored" -- is just plain arrogant.
In his post, loren went on to describe an environment where he was slowly pushed-out of the decision-making process. Where he went from being a passionately engaged team member to being a comfortably-paid code monkey. This was not just about getting bored -- his role in the company was changing, and his attempts to reverse the changes had little effect.
Sure, he could suck it up and adapt to the new role, becoming the best code monkey he could be. But maybe that didn't line up with his personal goals. Maybe loren quit because he wasn't being fulfilled.
Seems like a pretty smart reason to leave, if you ask me.
Lastly:
> "Burn out is just a rationalization for giving up early."
No, no it's not. This is a very dangerous line of thinking. If burn out to you means getting tired of mind-numbing tedium, you haven't experienced burn out. Actual burn out can be a very valid reason to "give up", or at the very least take an extended vacation. You can't just push through the physical symptoms of extreme stress and exhaustion, at least not without causing even more harm.