Is the writing incorrect or forced? is the statement idiotic?
Anyway: the entire thing is way longer (seven sections) and I'm still failing on translating it; but the main idea of calling them ghosts or doppelgangers is to adress the problem of identity and thus, in this case, of the authenticity of human relationships (later, for our possibilities of success attaining freedom and an ethical life). You could think about those so called ghosts like the Hari series (Hari II, Hari III, Hari nth) from Solaris, or Rei's vessels (Rei I, Rei II, Rei III) from NGE: as doubles wich are not the entities in themselves, but mere replaceable signs of them.
TL;DR The shit is complex and I'm still trying myself to get it clear.
Signs are linguistic (discoursive, psychic) replacements of things wich, while allowing us to attempt -at the best- a partial understandment of the actual world (by modelling it), at the same time turn it unreacheable and all interaction on/with it inevitably virtual, understood as mediated (by those very signs), biased, metaphorical, fictional... in one word: ARTIFICIAL; postulated, man-made and thus subjective, failable and unable to be taken as real.
Realism, as from Vienna Circle's final and most refined attempt of functional definition, means the possibility of grasping the syntax of an ultimate language wich would allow us to stablish a sort of bijection between discourse and the world: an univocal, complete and unique -safe an isomorphism- relation between signs and things from the world, finally erradicating metaphysics understood as signs without sense -in the world-. Such project was proven to be likely impossible by Wittgenstein himself in the following years, as a product of his late studies of Saint Augustin on the learning of language, esentially revealing the inexistence of atomic facts. The concept of sign used here also owes very much to Peirce's triadic conception of it.