In the earlier period, Uruk was in fact substantially larger, thus the quibble. Marc Van De Mieroop, The Ancient Mesopotamian City, p.37:

But many aspects of Uruk show its special status in southern Mesopotamia. Its size greatly surpasses that of contemporary cities: around 3200 it is estimated to have been about 100 hectares in size, while in the region to its north the largest city measured only 50 hectares, and in the south the only other city, Ur, covered only 10-15 hectares. ... And Uruk continued to grow: around 2800 its walls encircled an area of 494 hectares and occupation outside the walls was likely.