It is just "one" method of installation, and not even mentioned at the top of the page. The page also says

> Note The Microsoft Store package is currently considered unstable while its interactions with other tools and other copies of Python are evaluated. While Python itself is stable, this installation method may change its behavior and capabilities during Python 3.7 releases.

It is "an" official method, not the preferred official method, and most certainly not "the" official method.