There are a number of ways they're able to tell the difference between arrowheads and sharpened stones put on a stick, including high-resolution CT to look at the stress microcracks of the arrowhead. Bow-fired arrows and thrown spearheads have different launch stress profiles as well as impact profiles. There are a lot of overlapping types of analysis that happen to establish what technology did or did not exist in a given area at a given time.