If a man will misrepresent people who are still here, and talked to him, I don't see why he wouldn't just flat out lie about there being an Italian coven. Or maybe he did to them what he did to the Passamoquoddy.
I haven't read his book. Tell me, does he repeat the one about a Europe-wide witch-cult? (An unfortunate number of modern pagans do believe in that one, despite plenty of historical evidence that pre-Christian peoples had many different religious beliefs. Margaret Murray did neo-pagans no favors.)