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.
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.
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