It's not unlikely, in fact it's expected. The hypothesis of a virus circulating in August which eventually evolved into what is now SARS-CoV-2 is probably like

It's not unlikely, in fact it's expected. The hypothesis of a virus circulating in August which eventually evolved into what is now SARS-CoV-2 is probably likely (and surely more convenient), rather than the alternative hypothesis of a virus suddenly emerging perfectly adapted to humans and human-human transmission close to a laboratory that studies and specialises in such viruses.