Android Auto works for me only if I use USB cable to connect the phone.
It is unavailable with Bluetooth.
Is this expected?

 

Yes this is expected. As others have pointed out in other threads, Apple CarPlay and Android Auto don't use Bluetooth, they use WiFi. And while they are available in 3rd party stereos, they are quite rare in MFR systems as of now. I don't know why that is - it seems to take a long time for these things to trickle down to cars. Maybe it's because the integration and development time of cars tends to be pretty long compared to single-purpose consumer electronics.

The RDX does have a WiFi chip in there somewhere, which can be used to access updates or for on-board Internet connectivity, so I guess there's a chance that it could be upgraded in the future to allow for wireless AA or CP connectivity, but I seriously doubt that's going to happen.

 

Correct, as Waetherman also noted.
There is a lot of data being transmitted, and Bluetooth can not handle this much in a timely manner, if at all

Additionally, it will use a bit of battery so having it plugged in will keep you from having a dead phone battery.