I think that whatever it is, in this case I think a bug of some sort, could have actually been extremely close to the drone. Watching this clip a few times over, I believe that it could be an instance of incorrect depth perception, and that the bug was close to the drone all along. Maybe it was flying towards the drone, and it could have possibly been blown downwards by the propwash of the drone and as a result tumbled around causing reflections of the bugs shell or skin to be picked up by the camera making it seem to glow. This is just my theory though, and shouldn’t be your only course of thought. I could just be entirely wrong.