Your correction is appreciated. However, I would point out that at least some of those sources seem to say that the Christians were influenced by pagan notions. I have read James Scarth Gale and he seems to find the traditional beliefs in demons to be silly. The quotation above, I think, is not saying that the demon possession was real, but that the local religious beliefs were false. I could be wrong, but I have read enough of Gale, I think, to understand his view on this.