It's been many many, moons since Old Ben studied Anthropology but -- I don't think gender can be determined from just those remains.
Gender can be inferred from the size of bones.
But even with complete skeletons, sex estimates won't be 100% correct. With skulls alone, good bone folks can probably get in the low 90% range for a population.
The article refers to bone from a robust individual, very active.
Given sexual dimorphism [the fact that hominid males are typically larger than hominid females] perhaps they made this conclusion from this bone being larger than would be expected for a female of this species. Also, wouldn’t the activity patterns developed in the bone be different for an adult hunting male in his prime compared with those of a female living a less, or differently active way of life?