that registry is a mirror of npm's registry. the mirror contains all package data but does not include any of the permissions or user management, so this tool still depends on npm infra for both that, and as a replication source.
registry.yarnpkg.com is a proxy, it doesn't contain any package data except for what gets cached by Cloudflare. Just a Cloudflare'd "CNAME registry.yarnpkg.com. registry.npmjs.org."