The quote you posted is from the first section having paragraphs labelled 1-5. The quote is in #3, which is referring to the link in #1 above that. The link in #1goes to a download for Directx 9.0c, which is the "this Direct x" that will work for Windows 10, Windows 8, Windows 7, Windows Vista, or Windows XP.
The next section, which has bullets and not numbered paragraphs, specifically matches each version of Direct X with a version/(s) of Windows, which in addition to my quote I posted above, also says:
"Note: No standalone version of DirectX 12 is available. It's unclear at this point if DirectX 12 will also be made available for previous versions of Windows, like Windows 8, 7, or Vista."