It is interesting to analyse this in lieu of metaphysics of Kant and later, Schoepenhauer. I won't say I master the subject addressed by these philosophers. Far from it, I only scratched the surface and am just an amateur of the art.
But regarding the world within itself, or the world outside of human perception, there might not even be distiction between things we perceive so clearly as things in themselves, like the river bed and water, or air and trees.
All we perceive is a byproduct of experience and natural preconception of concepts like time and space. It doesn't mean, however, that what we perceive is false. It serves a orientation purpose and helps us guide ourselves in this world towards maximizing quality.
In this respect, paranormal activities might well be explained by outside phonomena. But just as separating what we normally perceive from what they really are has no practical purpose for us as humans (such is human experience, it imbues everything with human perception), observing such activities under the pure branch of rational observation misses entirely the point.
It doesn't really matter if those ghosts were real. Its effects were real not only in your psyche but also in the world (it evoked emotions in you that led you to selling the house). In this particular human aspect, they were subjectively quite real.