Got into a weird situation recently where my cheap android head unit was displaying Car Play from my phone, but (Google Maps) audio from my partner's. Directio

Got into a weird situation recently where my cheap android head unit was displaying Car Play from my phone, but (Google Maps) audio from my partner's. Directions weren't coming from my phone's speaker or the car, but testing audio in the Maps app did (from the car). Still not sure what combination of connections it had managed to get itself into!