If the concept of ghosts are disinformation, who's the person that intentionally planted this seed? Even if that's the case, you'd have to go back thousands of years at least.

You seem to be convinced that ghosts don't exist. Why is that? Note that absence of evidence is not evidence of absence. Among the millions of potentially fraudulent claims from people reporting to have seen ghosts, just one legit claim would suffice to contradict your premise. I don't know how good those odds are, but I'm guessing they're probably not as bad as you seem to believe.

On the contrary, the claim that "ghosts don't exist" seems to be a prime candidate for being disinformation. Pretty useful thing for secular institutions to have the population believe (regardless of its truth value) if only to wrestle power away from religious and spiritual institutions.