Also coming from a rookie programmer POV:
Its possible that each defender on the field has a "position", probably an x, y coordinate based on where they are on the field. When a pump fake happens it will check to see if each defender is to the right, left, or in front of the quarterback and they will react accordingly. Maybe a backwards pump fake causes all defenders to react for whatever reason, I would assume by mistake. I'm not sure what would cause them all to rush the qb, but that would be my best guess as to why they all react to it.