Assets = Liabilities (debt) + Capital (equity). The article was very careful to use the term assets, not market cap. Not too hard to put together a real estate investment company that ends up with $250B in assets especially in a country with a housing bubble going on, even if they have a relatively small market cap.
Good to know you focused on the housing bubble being able to prop that figure up because without the housing bubble in China along with their stimulus programs in place there would be no such thing as the number $250,000,000,000.