It may indeed be a California thing. Juglans californica, the California black walnut, is a distinct species from the black walnut found in the eastern U.S. The nuts are small and difficult to crack, and the meats are small, bitter, and generally not worth the trouble of extraction. I tried making nocino from unripe California black walnuts, and it was terrible. It wouldn't surprise me that the wood produces a noxious smoke when burned.