I don't think macOS comes with git; like, it might actually come with a git binary, but that binary is just a "shim" that runs an actual copy of git from an installed copy of Xcode. If you want to upgrade what is conceptually that copy of git you can thereby upgrade Xcode. (If you haven't installed Xcode then it might have come from a related package called Xcode Command Line Tools that doesn't include Xcode.app; if you run these shims and don't have Xcode installed it offers to install this package for you automatically.)
