I don't think they negate it. They state that it is unlikely, and then they note that the debate is not settled: "More scientific data could swing the balance

I don't think they negate it. They state that it is unlikely, and then they note that the debate is not settled: "More scientific data could swing the balance of evidence to favor one hypothesis over another. Obtaining related viral sequences from animal sources would be the most definitive way of revealing viral origins. For example, a future observation of an intermediate or fully formed polybasic cleavage site in a SARS-CoV-2-like virus from animals would lend even further support to the natural-selection hypotheses."