Depends entirely on the state/country, but some places have a law where a plot of land that is surrounded by other plots of land must always have some kind of accessible path to it, in the case that the surrounding plots develop around it and box it in, leaving no route for the landowner to actually reach it. Cyprus, for example is such a country where they do this. Germany, where this trek took place, probably has similar laws(?)

I actually don't know, but that is what was going through my mind when I thought "who would mark this as a public access path?"