http://www.abrahamicfaiths.com/WebArticles/MehdiRevealed.htm
The Arabs like Hebrews are a group of people united by a common language, Arabic, and do not necessarily require certain genealogic relationship for its membership, as many mistakenly believe. Despite such a relaxed requirement it is ironic though that Arabs prided themselves on their ancestry and for them Arab was the noblest of nations...
...the concept of Mehdi has evolved to give legitimacy of governance to different political groups of interest for clear political ambitions and has nothing to do with Islam. The Holy Quran and the authentic Prophetic traditions (Bukhari and Muslim) are completely silent on this topic. Therefore, Mahdi related traditions, which I proved are weak should be approached with caution. An interesting parallel with Jewish eschatology is obvious.
But, that is my point. The Luo are of the Omanis. There is a genealogic relationship. And the Mahdi is suppose to be a descendant.