Even if false, it's still a good book, and Greg is doing good work. Perhaps the story was a fiction created to explain the missing page in his passport to the US consulate? Considering how much he talked about Yak dung in the book, some of it might have made it's way into the story.
If you search for "K2 Pakistan" on
Google Maps satellite, you can follow his path off K2, find the river turnoff he missed, and the village where first built a school, and the bridge he built. (Down and to the left.)