Acral lentigious is most common type of melanoma in African Americans and is on the palms or soels. I guess the typical thinking of chest and back (sun exposed) is a little different in this type? Among all demographics; melanomas occur the majority of time on the limbs (~36% lower and ~19% upper); trunk is ~27%... So based on that and him being of African descent we can choose palms.
For more explanations and pictures: https://www.aimatmelanoma.org/melanoma-risk-factors/melanoma-in-people-of-color/acral-lentiginous-melanoma-alm/
I just think plams are not protected by the melanin and got this right.