The faster rider should stop and wait. The last thing anyone needs is some asshat buzzing their back wheel, descending is challenging enough, jeez.
Don’t do what I did once when i was young and foolish; rather than wait I kept bombing along. I was fast closing in on the rider in front. His friends had stopped further down the trail and warned him that I was coming through, and to stop and pull over. As I sailed past I nodded and thanked them for acquiescing to my superior skillz , misjudged how much space I had, clipped one of their pedals, sent two bikes flying and managed to deck myself.”Rad”.