Not at all, there are plenty of cases of confused property lines. I've seen it myself where an owner makes a line that is convenient but not accurate, could have been that way for decades. I just went through a whole pile of surveying last year on my own property and found that an old fence line was off by several meters. I was also hunting in an area last year where a new property owner placed signs on what turns out isn't their actual property, I didn't cross the markers at that time but confirmed through my surveyor that the area in question wasn't owned by them, they put the signs there because it was on a previously made trail.
Could also be the person that set it up was using an app that marked it as public when it wasn't.