That's most likely because Grok is powered by scanning tweets by other people on Twitter, and other people on Twitter will have been speculating about why Grok would be talking about the subject. Its rambling may or not reflect reality.
For instance, the last sentence in the screenshot is about how users have talked about Grok's unprompted mentions of South African issues, which it then credits to an indianexpress.com article it dates to March 25th. Unless the reporters of that site are time travellers, I'm not sure how they could be writing about Grok's white genocide opinions back then.
(To be clear, I'm not saying Musk or his lackeys didn't give Grok the instruction, I'm saying the only reason Grok is telling people this is because people on Twitter have been saying it. If people on Twitter had been saying that Grok was programmed by monkeys throwing jive at a dart board, Grok would repeat that also)