There is one, and only one strain of SARS-CoV-2
I don't think the article addresses the point right. Yes, there is only one strain of Sars-CoV-2 as the definition of a strain is a strict scientific term. Nevertheless, there are different clades [1] of Sars-CoV-2, which are characterised as organisms with a common ancestor [2]. This doesn't has to imply a changed property, like infectivity or mortality, but it implies common heritage which is of course of interest. You can see it nicely in the the phylogenetic tree of the sequenced genomes [3].[1] https://onlinelibrary.wiley.com/doi/abs/10.1002/jmv.25902[2] https://en.wikipedia.org/wiki/Clade[3] https://nextstrain.org/ncov/global