This isn’t really a mystery except if we think so. Ever heard of  making arrowheads out of glass?

This reads: “Knife and projectile points. In some instances, American Indian residents of the Village** used traditional techniques to modify imported objects. This piece of glass had one edge “flakes”…struck with stone or another hard object…to turn it into a sharp-edged knife. This same method is used to make stone tools, like these projectile points.”

** Fort Vancouver Historical Site