We are already the densest OECD city by quite a margin! (22,000 per sqkm in the inner 20 district, twice that of Manhanttan and 3 times that of Tokyo - and still 8,600 in the Petite Couronne, which includes 8 million people)
Yeah; they're probably thinking of New York City. If taken on its own, Manhattan is one of the densest cities in the world; the rest of NYC brings it down a lot.