You are correct. Any bit of property that you aren't personally in physical possession of is a social construct.

Social consensus is the only reason that you can leave your car at the curb, and come back to it a week later, and still expect it to be yours. Social consensus is the only reason that you can own land that you don't personally use. Social consensus is the only thing that prevents people working at your widget factory from deciding on Tuesday that its actually their widget factory, and that they would be better off by cutting out the middleman.

There are very rare, very extreme situations in which this kind of social consensus is very prominently broken.