Perhaps, when you die far from home, it takes a while for your spirit to realize that the body is dead, and move forward accordingly.
Metafilter user humanfont laid out a fascinating possibility: that the many encounters with Pippin in the Bob Marshall Wilderness were not with the living man Noah Pippin, but with his ghost. Humanfont goes on to recount one of his own encounters with a ghost while hiking in the high Rockies, an engrossing story which shares many of the hallmarks of the encounters with Pippin.
Tales of encountering a traveler in the wilderness, only to later learn that they had been long dead by then, are rife throughout human history. These sorts of stories have no doubt been told in every culture around the world. (Off the top of my head, I can think of versions from Celtic, Eastern European, and sub-Saharan Africa.)
Most often, the ghost is that of someone who died nearby. Sentient ghosts (those who look and act just like any other human being) rarely seem to travel far from their place of death. These days, in North America at least, the stranger you meet in the woods is likely to be another hiker, hunter, or fisherman. In the past, and in other parts of the world, it's more likely to be a traveler walking from one place to the next.
These apparitions are usually "fresh," in the sense that they are rarely seen more than a few years after their time of death. Most tales seem to involve people who died within weeks or months of their sighting. Perhaps, when you die far from home, it takes a while for your spirit to realize that the body is dead, and move forward accordingly.
As humanfont notes, "During the whole encounter it seems like something is off." The stranger may appear curt, and will probably refuse any offers of food or supplies.
Some areas seem to harbor more ghosts than others. In Pacific Northwest Native American tradition, rivers are often the location where spirits are found. In rural American tradition, an uninhabited crossroad is where you will meet the spirits of dead travelers. And throughout America you can find stories of spirits walking along the shoulder of the road, looking to thumb a ride.
One similar component to all of these stories is that they are the spirits of travelers who died accidentally. This delineates the difference between this type of spirit, and those you will meet at (say) Japan's infamous "Suicide Forest."