This is a motte and bailey. The article is about genetic engineering, not accidental leaks, so the specific lab leak theory in this context would be one where not only the virus, but it's subsequent mutations, were engineered and leaked. The probability of it being genetically engineered first for the leak and then for the subsequent mutations is incredibly unlikely and a soft, qualitative model of synonymous mutations is not up to the standard. Especially since the model takes first sequencing as direct evidence for location of origin (it isn't) and it doesn't take into account the mishmash of explosive spread, reinfection, superinfection, and chronic infection that isn't, to my knowledge, present for any other known virus - a strong quantitative model would be necessary at minimum.