Here's a google earth screenshot of the area:
The first 'lost' hiker we met said that he got lost in the hills above Mirror Lake. He said that he was following what he thought was the trail, but it ended up going to a campsite. Just beyond it he said there was a cliff.
From my trip report:
Before reaching Lone Pine Lake, we met someone who was descending without summiting. He had struggled up to Trail Camp and spent the afternoon dry heaving. After sleeping for the night, he felt better and had made it up to switchback 75 or 80. At that point he decided to turn around, but his friends continued on. On his way off the mountain, he said he got lost between Trail Camp and Mirror Lake, losing at least an hour.
The 2nd lost hiker was wandering around the hills to the South East of Outpost. If you're standing in camp and looking at the waterfall, he was to the far left.
We reached camp around 5:15 pm. By 7:00 pm we had eaten, repacked our bags for the summit attempt and had prepared for bed. I set an alarm for 1 am. If we slept well, the plan was to eat and leave by 1:30 am, in the hopes of being on Trail Crest to watch the sunrise.
We woke up and got ready as planned. To our surprise, a hiker had lost the trail and was yelling down to us from the hills to the left of the waterfall at Outpost Camp. When he saw our headlamps, he started yelling ‘Please help me, I’ve lost the trail,’ or something along those lines. We told him the the trail was ‘this way’ and to walk towards our headlamps. After about 30 mins, he made it to our camp. He had told us that he had been on the trail for 20 hrs and that he thought his ‘mates’ would be out there looking for him. It wasn’t clear if these were people he started the hike with or not. We made sure he had enough food/water to make it back to Whitney Portal and got him started on the trail down. It was 2:30 by the time we started hiking towards Trail Camp.
