I can only guess as you've not given much detail. There are several possibilities.
Pre 1994, Chinese (mainland) nationals were treated as 'non-whites' by (EDIT TO CORRECT) SOUTH AFRICA whereas ROC (Taiwan) nationals were treated as 'white'. You may have come across someone who remembers this old situation and is prejudiced - and wrong!
It may be that it is very difficult/expensive/impossible for them to obtain a work visa for you, or visas for other countries if your job requires you to travel. They would therefore prefer an EU/AU/NZ national.
Last edited by Capetonian; 24th Jun 2013 at 20:41.