Does the author have no experience with Android Auto? The same happens there, if the app is on my phone and it supports Android Auto then it will automatically be available in the car, along with all media on my phone. This isn't a CarPlay only functionalitiy, it's just how phone mirroring works on both platforms. Author seems to think there is an extra step involved on Android. Perhaps by "Play Store" they mean the car manufacturer's own app store?
Source: I use Android Auto constantly in my own vehicle and in the 15+ rental cars I have every year.