The article starts out by distinguishing between the "Passenger Indians" and the "Indentured migrants".  I would suspect that most of today's SA Indian merchant class are descended from the former.
I can recall that under apartheid, as a part of Verwoerd's "filing-cabinet" politics, aka "Group Areas  Act" (everyone in his correct designated place), Indian traders were chased out of CBD areas (unless they chose to operate under white "fronting").