They were either super day-hikers, starting at Onion Valley or Horseshoe Meadows, and exiting over Trail Crest, or lost hikers.
On my 5 night trip from Onion Valley to Whitney/Whitney Portal we encountered one of those "super day-hikers" as we descended from Forester Pass. He had started at Whitney Portal early that morning and planned on finishing at Onion Valley that night. His gear/clothes/water were ultralight.
