Greg said: "I'd be curious to know how they determine that they're tools and not
just
rocks." 
They have an assemblage, something like 140 cores and flakes, not just one or
two rocks. And fracture surfaces are distinctive, you see wave forms in the
cleaved stone radiating from the "bulb" where the impact occurred.
One way of making stone tools is to start with a big round stone. Hit it on one
side and knock off a flattish flake. The flake will be shaped into a blade of
some sort, or maybe used just as it came off the stone. Knock another flake off
the round stone, right next to the first one. Then another. Go round and round
the big stone, taking flakes off like taking leaves off an artichoke or slices
of meat off a vertical rotisserie. When the stone is too narrow to provide more
useful flakes, you have a "core." I think cores also have usefulness as tools,
maybe as hammers, but I'm not certain.

One or two stones might get naturally broken in a way that would leave you
guessing if it was a tool or not. But 140 cores and flakes all in one place? Its
tools, the product of deliberate manufacture.

TomConroyBerkeley