The development artifact described can most definitely result from stand or semi/stand devilment in extreme contrast conditions. I personally have seen it many times with semi-stand development in this type of lighting.
The most probable cause is bromide drag, but with this type of development it is possible that infectious development could well play a role as well.

The major point is I want to make, however, is that you don't have to move the camera to get this result.
Sounds interesting, happen to have any around for comparison?