I do not think that anyone is choosing a particular brand in religion, namely Islam.  I do not think that the Malays in Cape Town identify with being 'coloured'.  The ID book clearly carried the identity of the population before 1994  ie  00-White  01-Coloured  02 -Malay  03-Griqua 04-Chinese 05-Indian 06- other Asian 07-Other Coloured.  Malays who identify with being coloured are either from inter-cultural marriages or there may be confusion with Apartheid being the culprit.   It is also not about a withering Malay, but that as time evolve people do too and it may not be all that necessary to identify technically with a group  now in post-Apartheid.  The other reason may be that more Muslim people now choose unity as in one force in Islam, to being dissected.   It depends entirely on how you see yourself.   Criminal European human-traffickers who abducted and kidnapped people in the 19th century, stripped them of their papers and identity, hence taking on the surname of their employer