Do you mean the radio was off but turns on when you shut off the car, or that the radio was on and then stays on after the car is off? The latter is pretty much standard in cars lately. But the Bolt doesn't have an ACC mode so it could be just an alternative to that to let us sit in the driveway until a song is done. I haven't come across any menu item that can change that behavior but I didn't read every bit of the thick manual either.
I mean, let's say I have the radio on as I am pulling into the parking lot. I park and press the power button and it turns off the car, including the radio. Then in a couple of seconds, the radio turns back on. I haven't checked how long it stays on, but I know for sure that as soon as I open the driver side door, it turns off.
Yes, that's normal behavior and mine does it too. Turn off the car and the head unit shuts everything down for a moment but then the radio turns back on. Our Subaru does it too so I think its the industry standard now that there is no physical key to have the ACC mode we've been used to for decades.