“Auxiliary light on”
I guess they use that to trigger the drop.
That’s it. Some DJI models have that ‘auxiliary light’ which is just a led at the bottom of the drone, original purpose is to locate it easier and/or provide more light on where you’re going. As the drone doesn’t have any other ways to communicate with the payload they just tape light sensor on top of it and the payload-mechanism works independently from the drone.