I own land in this general vicinity, and part of the purchase process that the title insurance company covered when I bought it was ensuring that not only was I really purchasing what I thought I was purchasing, but that access to the land was guaranteed: I and all the plots around me have easements where a quasi-government entity guarantees roads that connect my plot to county roads, then state highways, then interstate highways.

I would say that if land was purchased that completely blocked off access to public land without such easements, somebody screwed up royally with regard to such easements. Not sure if that's what actually happened with the land in question?

edit: actually reading an article linked within the one linked here: "This is a murky legal area, due in part to the failure of Congress to ensure access to landlocked federal public lands". So yeah, someone screwed up royally and it was Congress.

It becomes landlocked and only accessible by land to the landowner(s) of the surrounding parcels. It is still accessible by air, but chartering a chopper is very expensive.

I’m not sure what rules there are if there’s a navigable waterway that goes into the public land through private land, there may be issues if you have to portage around obstacles on the river onto the private land. I would assume that if you can access the navigable waterway from public land, you are allowed to use it to reach the landlocked public land by traveling along the waterway through private land, but I’m not 100% sure.