LTE Sensor Gateway sample app

I was hoping to get an explanation of how the LTE Sensor Gateway sample app works.  The SDK documents the sample app here:

I understand that this sample app makes use of the lte_ble_gateway sample app for the nRT91 on the development kit, and the Bluetooth: HCI UART sample for the nRF52 board controller.  My understanding is that this makes use of the Host Controller Interface H:4 to allow the lower levels of the BLE stack to run on the nRF52 while the higher levels are run on the nRF91.

I think that in a real application, there is a need for only either the BT radio or the LTE radio to transmit at any particular time; they should never both transmit at once.  Does this LTE Sensor Gateway sample make use of some mechanism to make sure that the transmit of the two radios is mutually exclusive, and, if so, where is that handled in the code?  I wasn't sure if the BT radio in the sample app would ever transmit once the BT connection was made, or if it just received data from the Thingy.

If this is not handled in the code, do you have a suggestion as to how the code could ensure that the radios would never transmit at the same time?  Any sample code?

What is a design approach that could be taken where the situation was reversed, where the BT MCU was the host and the LTE MCU the host controller, so that the BT MCU would decide when something should get sent out on LTE?