The idea here https://github.com/openSUSE/installation-images/blob/master/data/boot/grub.cfg#L41-L47 was to first get the suse efi partition by looking for a file that's expected to be always there, then boot the suse specific grub2. It's of course prone to errors to look for one file and then use another one but the alternative would be to do a grub2 'search' for each suse flavor. And just booting the arch-specific default is not a good way either, as you have already pointed out.