Yeah, it looks like the device is so borked it will not run Harmattan.

However, as long as you can start ubiboot, you can use it with Nemo or SailfishOS.

Regarding your untar command, if I remember correctly the order of the flags matters, you need to put the "double-dash" options after the -f option, like this:

sudo tar -xvzf sailfish.tar.bz2 --numeric-owner -C /media/Alt_OS/

(of course it might depend on implementation/version...)

And moreover, I'd recommend you bunzip2 the file on your linux box, copy the resulting tarfile to forex. your partition 1, unmount partitions, go to ubiboot console, mount partitions 1 & 4, and then untar the archive on device itself with:

tar -xvf /mnt/1/sailfish.tar --numeric-owner -C /mnt/4/