It was the original author who issued the retraction, The Guardian just had enough credibility to follow up on that. That other news organizations lacked retractions does not make the original reporting of the author's claim any less retracted. If there are reports showing the retraction was bogus and there was separate proof contradicting the original author's retraction that would be something else of course, but you can't just say "I swear you'll find them, just keep looking harder!" or anyone could just make any claim up they wanted.

Thanks to mcintyre1994 for noting the link in the retraction does actually go into the details of why the author retracted the claim https://www.theguardian.com/books/2023/sep/12/elon-musk-biog...