I wonder if it could be related to an insect equivalent of grid cells, neurons involved in dead reckoning found in mammals. The firing pattern of a grid cell is a triangular or hexagonal pattern depending on how you look at it. Drosophila's ellipsoid body neurons have been shown to behave similarly to head direction cells so it's not implausible.
https://en.m.wikipedia.org/wiki/Grid_cell
https://en.m.wikipedia.org/wiki/Head_direction_cells