They likely used better equipment. I've done the same and a black co-worker explained that black hair is much coarser than white hair so they must use much sharper shears and keep them in top shape. Your typical (white) barber shop would use shears well past when they are too dull to cut black hair in an acceptable way but work well enough for the average white customer, but sharp shears leave hair much healthier and give a cleaner cut.