No ... I don't actually think so. A box pleat is a square type pleat, as apposed to an accordian pleat, which is more common. Box pleats are often sewn down to about the hips, but also can be loose from the waistband.
It might be Inverted Box Pleats:
Looking at this closely, it looks more like a gore (or a godet) ... which is a separate piece of V shaped fabric sewn in to a seam that has been cut open, to make the skirt flare.