Google HOME – Stream Music Without Casting From Phone

I am demoing a Google HOME and I am a happy Amazon Echo customer, so going to compare it to Echo.

I noticed that if I ask Google HOME to play music, it always appears to “cast” from my phone if we are on the same Wi-Fi. I heard it isn’t really casting but just a companion app to the phone. Yet that app does say “casting.”

If I turn WiFi off on my phone, Google HOME will simply stream without phone.

Is there anyway to turn this off when both devices are on the same WiFi?