I'm confused as to why they're saying that something 1/3rd the size of a human wouldn't be smart enough to make and use tools, etc. A 9 or 10 year old child weighs about 65 lbs., and they can use sticks and stuff like that.
Not to mention a crow is WAY smarter than many animals far bigger than it. Same deal with parrots. Brain mass VS total weight is a better indicator of intelligence than brain size, as otherwise wouldn't elephants and whales be a LOT smarter than people?
The do mention that their brain size is 1/3 the size of a modern human, but they are bigger than 1/3 the size of a modern human (I'd say worldwide average human weight is what, 140 pounds?, VS these guys at 65). Regardless though, it's worth noting they've recently proven chimps have the capability to learn to flintknap, so the whole argument seems a bit silly.