Back to the original question-
The bit of the wing you probably saw moving was the flaperon. On the 777 that lies just outboard of the inboard flap and as it's name suggests acts in two ways. At cruising speeds the flaperon acts as a high speed aileron with the left and right flaperons acting differentially. At low speeds (ie Approach) the flaperon acts as a flap with both left and right flaperons moving down together.
Hippo (If pigs can't fly then neither can I!)