IMO the taking down of flags is probably the cause of not knowing where the border truly is. Up until recently there were sections of the US/Canadian border where you could accidentally drive into the other without going through a passport check by making a wrong turn.
Imagine been a farmer in the middle of nowhere, why does this land here belong to me, but that land on the other side of the old rubber tree doesn't? You wouldn't care if you hadn't seen a government official in your entire lifetime, you'd just go and build a house and put up a flag.
Again think of it from the PoV of the soldier who took down the flag. You're following orders, you're told you're performing an operation in your own territory near the border. This is your country... you don't know that the top brass isn't entirely certain that it is and that they're relying on an American company to have reliable maps of their own territory.