This chart isn’t saying that there are more enlisted black women than black men, it’s saying that among enlisted women there are higher rates of black women than black men among enlisted men.

The split between men and women is about 80% men and 20% women in total so even black men’s enlisted percentage of 17% would mean something like 13% of total enlisted versus black women’s 29% is less than 6% of total.

Black people are still overrepresented in the military versus US demographics generally

It seems like among men, the racial category distribution is fairly even, whereas among women, White people are underrepresented whereas Black people are overrepresented.

My guess is because of overlap between racially segregated roles and traditional gender roles. One must further inspect the stats divided by roles to confirm.