Hmmm - long time since I have worked for a governmental agency where I had to learn about access, but the truth is probably somewhere between, and your sheriff probably more wrong than the kid, unfortunately. The law allows access to private lands for a variety of official reasons. However, some private property owners (Biltmore House, for instance) get a lot more property rights than others. Generally, it is simpler and better for get permission or and escort, but they are able to get their way in the end.
Simpler to hide or make it less appealing to come on your land.
The constitution might say a census is taken every ten years but where is the mandate for me to participate ?