Very good question. The article I'm reading says "Today, most independent researchers believe that the 1979 flash was caused by a nuclear explosion" What does yours say?
It sounds like early on the US government said it was inconclusive in order to not offend South Africa and Israel. But more recently, people have been saying it was a nuclear test.
> A December 2016 report by William Burr and Avner Cohen of George Washington University's National Security Archive and Nuclear Proliferation International History Project noted that the debate over the South Atlantic flash has shifted over the last few years, on the side of a man-made weapon test.[1] The National Security Archive briefing concluded:
>> A Central Intelligence Agency-sponsored panel of well-respected scientists concluded that a mysterious flash detected by a U.S. Vela satellite over the South Atlantic on the night of 22 September 1979 was likely a nuclear test.
> The newly released research and subsequent report was largely based upon recently declassified documents in files at the National Archives of Gerard C. Smith, a former Ambassador and special envoy on nuclear nonproliferation during Jimmy Carter's presidency.[1][60][5] Smith had once said: "I was never able to break free from the thought that the event was a joint operation between Israel and South Africa." The documents cited a June 1980 U.S. State Department report where Defense Intelligence Agency Vice Director Jack Varona had said the ensuing U.S. investigation was a "white wash, due to political considerations" based on "flimsy evidence". He added that the "weight of the evidence pointed towards a nuclear event" and cited hydroacoustic data analyzed by the Naval Research Laboratory. The data, he suggested, involved "signals ... unique to nuclear shots in a maritime environment" and emanating from the area of "shallow waters between Prince Edward and Marion Islands, south-east of South Africa".[1][5][60]
> In 2018, a new study made the case for the double flash being a nuclear test.[6][7][61][62]
The quotes that it was a test were from journalists, and from people who "heard" about it. None from actual scientists who studied it.