There was always a small percentage of what had survived the purges of the church, so some of the 'satanic' practices probably were inheritors of the pagan traditions.
However the confessions of people under torture depend on the questions asked.
There is no evidence that any pagan practices survived that long, actually, except in the baltic area which was christianized very late. And even then it was practically extinct within 2-3 centuries.
But yes, the key there were the questions asked. Why the Malleus Maleficarum boosted belief in witchcraft was basically that it was a uniform set of "yes"/"no" questions that everyone asked, and every one got a yes to every one of them. (You'd get tortured until you said "yes" anyway.) Which in turn was taken as confirmation that it is an objective thing, since so many people who never knew each other were confessing the same things.
There is no evidence that that list came from anywhere else than Kramer's deranged mind. (Sprenger is thought to not have actually written anything there, and was likely just added as a more respectable authority.)
Also, the actual text doesn't contain any clues to some actual religion or belief. It's largely a work of an extreme mysoginist, and reflects that more than anything else. His justifications for witchcraft there aren't religious or continuation of (by now extinct) pagan traditions, but basically women being weak and carnal and all around evil and eager to sell their soul to the devil for little more than a little sex. An actual description of an ancient religion would have more to do with fertility rituals, appeasing the land spirits, and generally more practical purposes than getting boned by the devil and causing misfortune for the heck of it.
@I Am The Scum: Actually teenagers likely had nothing to do with it. Virtually everyone persecuted was mature by the standards of the time, or most actually old widows. Also the teenage rebellion to be accepted as an adult simply didn't exist at the time, as you'd be considered an adult, with all the responsibilities that come with it, usually actually before you hit puberty.
@Cainkane1:
1. Methinks you give Kramer and Sprenger too much credit, though. While they did formalize the list, the idea that all bad stuff (including diseases, storms, etc) comes from humans who exercise their free will to serve the devil was inherent in Christianity since at least Augustine. And various beliefs to that end existed long before the Malleus Maleficarum, albeit not so elaborate and not such a mass hysteria.
2. I don't think it was as much "leaked" as out in the open from day one. The reason the Malleus Maleficarum caused such a hysteria, was that it was the first such BS compendium to be mass-printed using the newfangled printing press. In the first three decades alone some twenty editions of it were published and sold like hot cakes. Everyone who could read and wanted a copy could get one. Basically it wasn't some secret inquisition manual, but something whose most pernicious effect was "educating" the population at large about the "dangers" of witchcraft.
3. I'm not sure if it's entirely correct to give the RCC the full blame. While Kramer was an inquisitor, and the church does have the complicity of not stopping him, it wasn't an activity particularly sanctioned by the church. Even the papal endorsement included in the book seems to actually be a forgery, and most of the church academics and theologians actually condemned the book. And the Inquisition never got the official duty to hunt witches, and at times was even forbidden to do so. (Most of the church's problem at the time were muslims and jews reverting to their own religion after being baptized, plus these newfangled protestants.) Most of the witch hunters were actually rather secular pyschopaths, or the odd priest overstepping his authority, rather than an RCC policy.
