App bundles allow smaller apk sizes [0]: > Google Play uses your app bundle to generate and serve optimized APKs for each device configuration, so only the code and resources that are needed for a specific device are downloaded to run your app. You no longer have to build, sign, and manage multiple APKs to optimize support for different devices, and users get smaller, more-optimized downloads. But as all this logic s…
1) google just sign these apks with their own certs.
2) google should present the developer with a google public key that the developer signs, allowing google to sign an apk with a google key that had a chain of trust to the developer.