Herotodus mentions a nation of pastoral herders who challenged Cambyses and whom he described as youthful and living to very venerable age and of great stature. The area he describes them as living is very confusing as well and I find it hard to pin point a general area of sub-Saharan Africa which he seemingly describes.
We can't tell if they have any connection to real, existing people, and we should probably assume they don't. Herodotos travelled widely, and certainly visited places like Egypt and Skythia, but his descriptions of peoples become increasingly vague and incredible as he takes the reader further towards the edges of the world. Beyond the Skythians in the north he supposes a wild people called Man-Eaters; beyond the Indians in the east is a land of wonders like dog-sized gold-digging ants; and beyond the west (as he thought Ethiopia was located) is a land of tall, strong, beautiful men called "Long-Living Ones" (Makrobioi). These men are supposed to choose their leader based on his height and looks, and to live to the ripe old age of 120. Even if there was a wealthy Ethiopian kingdom that made diplomatic contact with Kambyses, it seems clear that Herodotos' account of them is more legend than fact.