I was interested to discover that Android Auto will make Bluetooth and WiFi connections to your phone, just to be able to send and receive on both at the same time.
I wonder what the breakdown is, it probably wouldn't separate audio packets across protocols, maybe one gets relegated to instructions and metadata and the other is dedicated to audio? Or along service lines with different throughput requirements, like Maps on one and Spotify on the other? Or heck, maybe one is just for handshakes to establish the other.

Bluetooth does seem fine for handling audio, and at handling many devices simultaneously, so neither of those seem like good candidates for pulling WiFi in.

I could just look this up but I'm enjoying thinking about it.