Actually Poltergeist means "Noisy" ghost. From the Germany "Poltern" (to make noise) and "Giest" or Ghost.
For a full explanation please see the excellent Wiki article here:
Wiki Page
You actually bring up a excellent question with the RSPK, and I don't think the question is limited simply to Poltergeist activity but any paranormal activity in general.
The question being this. When we have physical response to paranormal activity, is it really the spirit itself which is manifesting the physical response? Or is it somehow using some dormant part in our own minds which has Psychokinetic capabilities to manipulate physical objects?
The same question could arise in instances where there is physical evidence often attributed to demonic entities. Scratches, Whelps and other physical manifestations which appear in those instances. Are they caused by the entity themselves, or are they produced by our minds which are being harassed or controlled by these entities.
There has been considerable research into the phenomena of hypnotic manipulation. One instance is where a hypnotized subject is told that their hand is being placed in boiling water when in fact its just placed in room temperature water. Out of those cases, 10% go on to form some manner of blistering on their finger or hand. Reference Article
HERE
Could the same type of thing be happening in some cases where it pertains to the paranormal. Great question and great topic. Thanks for bringing this up.