Homeschooling presupposes receiving education at home. K12 is not homeschooling. It’s also not free.
It is funded by taxpayer money since it is a public school program through which you get enrolled in a school in your state. This program follows all the requirements that exist for the regular schools and all the legislation. It’s just public school education you get online.
It requires some level of control over whether your children study at all and what exactly they’re going to be studying.