Although there are semilegendary views about early Kanuri roots in Yemen, little is known of the earliest phases of Kanuri culture. Contemporary Kanuri are the descendants of the ruling Saifawa family of the Kanem Empire. As a result of civil war, this family left Kanem in the fourteenth century and, after nearly a century of internal strife, established a new empire southwest of Lake Chad. This empire was and is known as Bornu, although Borno is now its official name. The area to which the Saifawa moved was inhabited by various peoples about whom little is known. Now they are known collectively as the Sau—reputedly a race of giants. For a period of several centuries, the efforts of the Saifawa to consolidate their power and expand their kingdom's boundaries led to the incorporation of many distinctive groups within Kanuri society. This process has not ended. Intermarriage, commerce, politics, and other factors have combined to produce a people who are culturally heterogeneous.
The Kanuri have had a strong influence on surrounding peoples, which include the Budum of Lake Chad, the Mandara and Kotoko (or Mogori) who live southeast of the Kanuri, the Marghi of the Damboa district, the Babur in the hills south of the Kanuri, the Bolewa located southwest of the Kanuri, and the Bede of Gashua, within the Kanuri territory. All of these groups have acquired various aspects of Kanuri culture, mainly the Kanuri language and Islam. Many, including the Hausa, were at one time subjects of the Kanuri Empire.
One thing about this article however is that it fails to mention how the Kanuri and their brother ethnic groups (ie Kotoko) descend from the Sao Civilization (found near lake Chad by Cameroon/Chad border). Studies show that the site flourished around the 6th Century BCE; and was inhabited long before that. It has even been concluded by some that the Sao civilization is the legendary country known as "Agisymba" to Greek scholars/geographers such as Ptolemy. Apparently, Sao/Agisymba was subdued by the Garamantes empire established by the Berbers after prolonged fierce battles. The Kanuri were NOT influenced by Arabs. They are purely INDIGENOUS/NATIVE in every sense of the word. Please avoid 'Arabizing' Black civilizations, it gets us nowhere and it doesn't pay credit where it is properly due!
i'm Abba Mai Saje, from Yobe state and I think I can answer your question, because i understand that the first sentence or phrase meaning is, the history of kanuri all of it, is legendary, full of braveness and worriors, so he {the writer} refers to all of the legendary history of kanuri are lost but half-legendary, and only few facts remain that are related to yemen.
And you say that kanuri are presently living in yemen that affirm connection, this is not enough to be affirmed because they may have immigrated to yemen or they came from somewhere els.