As so often, that news is not really news and the article exaggerates. That the countryside surrounding the cities was not empty has been known for decades. The image shown is not of some new discovery, but that of the city centre of Tikal, known in Europe at least since 1850. As the article itself explains later, the "ten of thousands of structures" consist mainly of roads, small dwellings, quarries and irrigation systems. Without actual excavations to gather concrete evidence, the population estimate of 10 million is pure speculation. That said, the LIDAR technique does make those excavations easier.