It seems like you think this is some standalone law rather than an integral part of the system that is able to create the concept of "owning" a piece of land to

It seems like you think this is some standalone law rather than an integral part of the system that is able to create the concept of "owning" a piece of land to begin with. The fundamental problem here is that both of these real estate owners did not care about "the line" enough to ascertain where it actually was, until a court finally had to do it decades later. The straightforward way to avoid that is to head off any such ambiguity ahead of time. Also in the context two-thirds of an acre doesn't seem like that much - it was seemingly only one eighth of what the plaintiff was looking to sell. The NPR long-form interview format is lacking in that it pushes out a bunch of pertinent details, but I'm guessing that was either goat grazing area outside the pen and/or the plaintiff/grandfather had already subdivided it into building lots and the judge saw using those lines as a straightforward way of settling the matter for a pro se defendant?