> If the distributions of bone densities among “people you would visually identify as ‘race X’ ” and “people you would visually identify as ‘race Y’ ” differ, then knowing that an individual would be someone you would visually identify as ‘race X’, gives you some amount of statistical information about their bone density.

Only if they differ substantially. If they look like https://evergreenleadership.com/wp-content/uploads/2014/01/B..., you can't conclude much from an individual's bone density measurement, even if "people of race X have 3% more bone density than people of race Y".