This is an absurdly hopeful balderdashery of an argument. There is no possible way to link biblical "witches", as a class, with some random pile of ancient graves in any manner that wouldn't be laughed out of court.
Even if they aren't linked, both spiritism and child sacrifice were cited as reasons for God driving the people out of Canaan. The reason given for killing "spiritists" is that they will "defile" you. No specific reason is given for killing witches but witches do often engage in spiritism. Therefore it's reasonable to include witches as a subclass of spiritists.