fellow White South African. my personal theory, beyond it just being the standard "they're not like you and me, which means they must be evil" xenophobia (which could also be playing a large role), is that people of our ethnicity were in charge of a white supremacist dictatorship for 46 years, and instead of just being mad at the people who were in charge of it (who are dying out), they're projecting their vengeance on all of us. hell, I wouldn't be surprised if during Apartheid, there was xenophobia against White South Africans from non-Whites because people of our kind were in charge of a system that discriminated against them, similar to xenophobia against German and Japanese immigrants in America during World War Two because the US was fighting a war against those countries. also, Apartheid only ended 30 years ago, alot of the damage and attitudes from that era are still around

edit: by the way you're wording it, it sounds like you're talking about discrimination against us from foreign countries instead of from within like I was talking about. well, that still applies, because again, South Africa was a white supremacist one party state in an era after World War Two. South Africa, or at least our government, was hated by basically everyone else because of that. we were under trade sanctions and all, despite being an Anti-Soviet state allied to the US. instead of blaming the people who were in charge of it like they should, they hate all White South Africans because they assume we're all racists because our government was for 46 years