That number is misleadingly low, because it doesn't include Next.js which bundles the dependency. Almost all usage in the wild will be Next.js, plus a few using the experimental React Router support.
As far as I'm aware, transitive dependencies are counted in this number. So when you npm install next.js, the download count for everything in its dependency tree gets incremented.
Beyond that, I think there is good reason to believe that the number is inflated due to automated downloads from things like CI pipelines, where hundreds or thousands of downloads might only represent a single instance in the wild.
As far as I'm aware, transitive dependencies are counted in this number. So when you npm install next.js, the download count for everything in its dependency tree gets incremented.
Beyond that, I think there is good reason to believe that the number is inflated due to automated downloads from things like CI pipelines, where hundreds or thousands of downloads might only represent a single instance in the wild.