::I have never heard of any Lemba claiming themselves being superior to anyone. All of the books, articles, videos about them show that they recognize that they are not legally Jewish, only ethnically at this point. They recognize that their ancestors walked away from the Torah based path a long time ago. Their main thing has been to trying to reconnect with their ancestral past and then decide what that means for their future. 

 ::As far as the time that it is thought of when their ancestors left Yemen. The Lemba didn't know. Their oral legends simply told them who some of their ancestors were and the name of the place they came from. They didn't know where that place was. It was through their contact with Professor Tudar Parfit that he was able to piece together where their ancestors came from. This was done by him traveling to the places based on the Lemba oral legend, and other sources as well as DNA testing done on the Lemba, known Jews, and Yemenite Arabs. 

 ::On another note it is known fact that the Lemba's ancestors mixed with Bantu women over hundreds of years. That is why some of them don't look that much different from other Bantus. Rabbinic scholars don't have a problem with the existance of the Lemba. The Lemba would essentially be what is called Benei Anusim. 

 ::I think it is easy to see that this article has not been fully written. Also, there is not a lot of information outside of the research that links their ancestors to anciently being Jewish mixed with Bantu.