It sounds like he already had linux running on the device, it just couldn't control/access everything, which was the ultimate goal of this project. So once you have linux running, even without being able to control everything, you have code execution. It seems like there'd be other ways to get the bootloader out, but I'm not familiar with the project, presumably he did the easiest thing he could do - or most interesting.
Considering spez has shown before he doesn’t really care for Reddit’s rules that are applied to the rable and he can do what he wants (like editing others posts), I fully expect the permanently blacked out subs to have new ownership and become public again before too long.
One time during a summer camp at my middle school I won a paper airplane contest with the basic because time aloft was a major contributor to scoring and a gust of wind caught my plane after I threw it and held it in the air for a while.
I mentioned after I'd won that I felt bad, it was luck that the wind came when it did and held it the way it did and the judge replied that other planes might not have caught the wind like mine did because mine was designed in such a way that it caught wind better.
The prize, ironically, was a book on how to make paper airplanes. I felt like that should have gone to the loser, but it was still cool.