I suspect this is a "tank vs sky" problem. The article says that the bright areas of bone are not the most important for predicting race. What if it's some features of different hospitals and x-ray setups?

Also did they release their code and anonymized data? If not, it's impossible to tell if this is a bug.

If I got this result in my work, I would check it 10k times over because it defies belief. Even allowing subtle skeletal differences in different ethnic groups, the differences in this case are not in the bone and at least sometimes not visible to the human eye. Unless there is an undiscovered difference in radio-opacity across ethnicities, the result doesn't make sense.