The paper then concludes that SARS-COV-2 must be a result of natural selection. While I think this is possible, they ignore the possibility that the virus is a result of artificial selection. If a laboratory were studying how SARS-COV-2 could pass to humans, they might serially pass the virus between mammals (like pangolins) in order to artificially select for mutations.
That is, in fact, exactly what previous scientists did in a 2012 experiment with bird flu. They wanted to make it transmissible between mammals, so they serially passed genetically modified bird flu between ferrets until it was. I wrote this up on my blog:https://get21stnight.com/2020/04/14/why-do-some-viruses-cros... . The result of this is that bird flu acquired previously unknown mutations in order to pass between mammals.
I'm not saying this is what happened, and there are some key differences (i.e. in the bird flu experiment, scientists had to start off with a genetically modified virus). Still, I disagree that we can definitively conclude this was a result of natural selection.