Pueblo Bonito, a six-story structure in Chaco Canyon, contained up to 600 rooms, making it the largest building in North America until the first skyscrapers rose in New York some 800 years later. Mayan civilization is believed to have supported a population of more than 10 million people at its peak between 250 and 900 A.D.
forgetting about mesoamerican pyramids in one sentence and then mentioning some of the people who built them in the next; somehow this glaring mistake makes me want to dismiss the article all together because i have no way of know what else they're getting wrong.
It seems that they got it from the wikipedia article on Chaco Canyon, which gives a couple of citations for this claim. Perhaps they meant by area or by overall volume, as opposed to by height? I don't know about volume because I haven't done a comparison.
https://en.wikipedia.org/wiki/Chaco_Culture_National_Historical_Park#Central_canyon
The central portion of the canyon contains the largest Chacoan complexes. The most studied is Pueblo Bonito. Covering almost 2 acres (0.81 ha) and comprising at least 650 rooms, it is the largest great house; in parts of the complex, the structure was four stories high.
Perhaps it's largest as measured in floor space, which is how we usually measure it these days. This seems to be implied by counting "rooms". Unfortunately my education was so poor that I don't even know off-hand whether any ancient mesoamerican pyramids had more floor space than Pueblo Bonito.