Mostly correct. It won't overwrite the kernel, but because it is located in /dev/mtd. /boot does get overwritten, because that it is part of rootfs.This means the kernel from the rootfs backup will be placed in /boot during restore. Nitdroid requires multiboot. So the part describing multiboot applies. The nitdroid kernel used for flashing is in /boot (just like the other kernel images) /and/ is the filessystem used by nitdroid itself.