From what I gather, a industrial-scale air-conditioning unit company basically broke the space open, since they were essentially doing large scale prefab construction already.

Just think about it from first principles. You can build large structures out of prefabricated parts, and if you design the parts sufficiently well, it's possible to fit them together fast. The problems are stuff like weight (transport costs start to dominate), volume (if there's not enough demand for skyscrapers, you don't want to be sitting on a skyscraper factory), etc.

In East China, they have a lot of structural advantages: a huge, hugely dense population, a government that loves big construction projects, a massive housing market, a great deal of experience in doing civic infrastructure fast, etc.