If a Bluetooth connection has been established, first the connected device will use it preferentially. The USB connection can be selected as an alternative. If you have two devices connected, one with Bluetooth and the other with USB, you can select between them on your two devices by playing one or the other.
If no Bluetooth connection is established, and the top LED is flashing blue and red (waiting for a Bluetooth device to pair with), plugging in a USB connection that isn’t a charger will shut off Bluetooth.
