Can ghosts in Harry Potter be touched? Mistake by J.K.R.?

"Pelting" could mean that Peeves through them in her direction and they went through her, thus causing her grief. Technically Peeves is a ghost too; a poltergeist is just an extreme troubling ghost, right? So in that sense, ghosts can, if they want to, attain the ability to hold things and be touched as if they were solid beings. At least, that's what I could gather from this all.