Jeff, is not necessary to use the microscope. A magnifying glass is more convenient.
Look the surface emulsion and base film under a reflected light.
If these surfaces seem flawless (no scratches or deposits), then it was a mechanical pressure which resulted in negative exposure in the yellow layer. In that place will result in more yellow color negative, and positive will be more open and blue. The negative traces of rubbing are not seen on emulsion because film processing cover the traces.
After me, the rubbing done by manual handling of the film, not the machine or camera. Faults are not straight.
The film goes through many hands. You choose.
I personally do not think that defects comes from electrostatic discharge damage. Ought to be larger and more visible.