I'm not sure where you got that from, that's for the iPod models that are actually supported by Rockbox.
This one, isn't.
It relies on a third party bootloader not sanctioned by Rockbox at all in any way, the installation of which completely removes the original firmware partition because dual boot is not possible currently and the additional space is more valuable to the user than a firmware they can't use.
You need to refer to Freemyipod's instructions and support for uninstalling the emCORE bootloader and Rockbox on this device.
[Saint]