Primitive people tend to adapt things from other cultures for their own uses. In reading about Ishi in books written by Saxton Pope, Ishi continued to knap arrowheads out of stone or volcanic glass after coming to live with white people, but favored our manufactured dowels over arrow shafts he could make on his own. For other Indians, it was no doubt easier to work the iron brought by the Europeans than the native stone. I don't believe American Indians had the capacity to manufacture iron prior to the arrival of Europeans, so all of their arrow and spear points were probably made out of stone or volcanic glass.
There are still many thousands of arrowheads made out of stone or glass that one can find around the countryside all over the US that were shot by Indians over the millennia.
I'm not sure what you mean by an "earlier people" than the American Indians. My understanding is that some people migrated over the Bering Strait, while others may have sailed over the Pacific, but once they got to America, they were all considered to be Indians from that point on. There is no record of any earlier people, such as Neanderthals or other types of hominids that may have existed prior to Homo Sapiens, in America (other than folk tales, of course).