Let's be honest, unless you use a private NPM registry, "react" means https://www.npmjs.com/package/react. GitHub should use the standard resolution algorithm as employed by npm/yarn (the CLI tools).

That's not the package.json that gets published in the npm react package. This one is what you're looking for:

https://github.com/facebook/react/blob/master/packages/react...

Just a standard dependency on version 15. It figured out react-dom just fine though.

  {
    "dependencies": {
      "react": "^15.6.1",
      "react-dom": "^15.6.1"
    }
  }