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?
Those are indeed the types of considerations that I would expect the experts to be using.
There are a variety of shape differences in the bones between male and female, but I don't think the tibia (the article said "shin bone") has many of those.
I would guess that size and muscle markings may have been more important. (But then I haven't studied fossils since grad school, so they may have something new.)