From what I understand, the author said he did not think it was likely to be natural, and did not say for certain it was man made. Also, I'm not sure if the author had the experience to make such a determination.
I listened to a group of virologists over the weekend who said it was NOT man made.
It has been identified through genome sequencing by several labs outside China, using their own patients to collect samples.
The Pasteur Institute - Paris was the 1st
https://www.pasteur.fr/en/press-area/press-documents/institut-pasteur-sequences-whole-genome-wuhan-coronavirus-2019-ncov