Or, maybe the outboard pivot joint failed and released, then the airflow has ripped half the control surface away; separating near the next pivot point?
I wonder if the outboard pivot was not lubricated and became stiffer and stiffer and eventually fractured when the elevator was moved, or possibly previous damage was caused from frozen de-icing fluid - not in Africa, obviously, but elsewhere perhaps?
All that aside, the Captain's decision seems to be extremely questionable :
......The captain decided to continue flying to Kinshasa requesting only right-hand turns. ........
Really ?