The Somalis, weary of the destruction inflicted on them went to the Imaam (Imaam Axmed), led by their (chosen) leader Hirabu. The Somalis with their leader concluded a complete peace with the Imaam.
After this, the Imaam made preparations for Jihad against Abyssinia, assembling his troops and the Somalis with their leader, Hirabu.
Finally, the 2003 abridged source that you are quoting says:
After this, the Imam made preparations for Jihad against Abyssinia, assembling his troops and the Somalis with their leader, Hirabu
which you conviently left out.
In summary, Somalis had 2 main leaders, Imaam Axmed Gurey and Imaam Nuur ibn Mujaahid. One main chieftain Hiraabu and several mini chieftains such as Garaad Daawuud of the Habar Magaadle and Garaad Mataan of the Gerri Koombe.