This is missing the biggest piece: phylogenetic analysis. They aligned a selected group of mutations and then eyeballed the alignments and then speculated.
Given what we know about the infectivity of Omicron, the combinatjion "Omicron was around in 2020" seems pretty astonishing. Combine this with "Omicron variants were formed by an entirely new mechanism that cannot be explained by previous biolog" and I'm going to suggest that the most likely explanation is that they cocked up their data somewhere.
I'm not qualified to peer review this - and it looks like no-one else has yet.
zenodo.org
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