There are three key versions (and several others; they have 1.0 through 1.6 and 2.0) of .NET Standard referenced; the key versions are 1.5 (supported by .NET Framework 4.6.2 and later and .NET Core 1.0 and later), 1.6 (supported by .NET Framework vNext and later and .NET Core 1.0 and later), and 2.0 (supported by .NET Framework 4.6.1 and later and .NET Core vNext and later).
Also, rereading the article, I notice "When we shipped .NET Core 1.0, we also introduced .NET Standard."
This text really could do with a good editor.
I think the versions prior to v1.6 were retrospectively defined based on the common capabilities of pre-existing platforms; v1.6 was what .NET Core 1.0 supported and .NET Framework vNext will support (2.0 is what .NET Framework 4.6.1 supports and what .NET Core vNext -- and vNext of MS's other platforms -- will support, and beyond 2.0 there will be more synchronous development across different platforms.)