From what I understand the article is referencing the entire lower limb which in medicine = the whole leg, relative to body mass. So the article does not seem to differentiate between femur length or lower leg length, just the lowere limb as a whole.

It is true that biomechanical differences exist. It was (I use the past tense because I have not been in contact with this type of research for a long time) believed that people of African descent had a biomechanical advantage in running due to limb length and pelvis angles. That is one of the reasons, back in the day, that it was thought that a caucasion would never out run an African. Simple genetic biomechanics. I don't know if this research or theory has withstood the test of time. I've been out of the feild for about 14 years.