This issue I described just happened prior to posting it. It is Poweramp only that does this. Other mobile apps that I have installed have options to disable bluetooth, but Poweramp does not. This is the problem.
The scenario was that Astiga cloud player was running and playing audio when I started my vehicle. Poweramp was not running at all. It must have some background processes that I will find and disable if at all possible. I started my vehicle, and Poweramp out of the blue decided to launch and takeover Bluetooth streaming. The one and only way to stop this is to uninstall Poweramp. Nothing else works.
With Poweramp uninstalled, Astiga streams over Bluetooth that is what I want to happen. I hope this is clear now. Per the first reply, there is a BETA feature that I am surprised was not added long ago that will disable Bluetooth from Poweramp.