He was just giving his opinion based on what he has read. He conducts his own tests, though, and is surprised by the results.
As far as how anyone knows that some arrowheads were ceremonial, I think the idea is based on artifacts that have been found with burials. The arrowheads are often very high quality. I think the idea that a hunter or warrior should have the best equipment in the afterlife was common, so it's not hard to see the connection. But, like you, I don't think we can rule out the idea that high quality (or very delicate) arrowheads were used everyday just like all the rest.
