What if the dirt itself is older than the stuff around it? Like people always talk about stuff moving sideways or getting dug up, but nobody brings up that a site can have dirt from somewhere else completely. My uncle worked on a dig where they found a layer of soil that came from a riverbed miles away, dumped there ages ago by some old flood. So your friend's "wrong" date might not be wrong at all, it might just be dating the dirt instead of the people. That's the thing nobody checks first, they just assume the ground stayed put. Half the time the ground is the newest thing at the site.