Well, I assume he ran a chroot of ArchLinuxARM stored on a loop-mounted image in the userstore.
Then you just start an X server after killing lab126_gui. Or displaying applications on the default DISPLAY.
This guy did it too:
https://www.mobileread.com/forums/sho...ght=arch+linux
But other people have done the same with debian armel.
...
Aside from the inherent coolness of running Arch on my Kindle (it is already on this laptop), there isn't much point.
Really, I prefer using my Kindle to read books.