One of the many ugly secrets of that ugly death cult, Islam, is that Arab racial superiority is one of its fundamental assumptions. These are Arab Muslims trying to put down African Muslims; of course, they had centuries of practice with this during their years as the biggest slave-traders in the world.
When you look back over the depressing history of Islam, one thing you will notice is how often Arab Muslims have attacked other Muslims, often with the excuse of restoring "Islamic purity" to less fanatical cultures. Yet Arabs as a whole have got to be one of the least productive groups, with the most primitive culture, on the face of the earth.
I don't think the Muslims in Darfur (or anywhere else in sub-Saharan Africa) "assume" that Arabs are "racially superior."