The harsh truth is, and I know this from spending the majority of my life living in a predominantly black part of London, at a predominantly black school and hearing it more times than I could count; a lot of Caribbeans and West Africans seem to think that Somalis, or East Africans in general, are inferior in some way, and they don't want to be associated with them, and so say that in an attempt to disassociate themselves from Somalis.
It's *******s obviously, but that's how a lot of non-East African black people I've come across think. Not all, but a lot.