Gold has implicit worth as an alternative store of value. You can buy gold, keep it in a safe or safe deposit box until you need it, carry it around in your pocket, or even on your wrist. It's convenient as a form of non-fiat currency, costs almost nothing to maintain, is functionally infinitely divisible, is fungible, and has reliably kept its value, gaining some during downturns when it may be a more reliable store of value than fiat currency (cash). Further, gold is immediately recognizable as valuable, easy and inexpensive to verify (any jeweler can do this easily), and has an agreed upon value around the world.
Real estate is none of these things. You can't store a house somewhere safe, you can't keep it in a safe or in your pocket, you certainly can't carry it around, it's a troublesome store of value because it's incredibly illiquid, it's expensive to maintain, it's expensive to verify as valuable, and if you ask 5 realtors from each of 5 different cities to price a property, you'll get 25 different answers. Further, you can't cut a small chunk of a house to sell if you need quick cash, and I'd hardly call selling any piece of a house quick.
A house is not a very useful store of value, therefore, and as such has two uses:
- As a home
- As an investment
You could live in it or store things in it, using it as the first, you could buy it and hope it appreciates, using it as the second, or you could rent it out, using it as the second while someone else uses it as the first. Either way, its value comes from its usefulness to be lived in, or its usefulness as an investment. Gold, meanwhile, derives its value from its usefulness as a store of value, and to a smaller degree from its usefulness in industry. Notice the difference here, where usefulness directly impacts the price of real estate on a property by property basis, whereas usefulness is fairly unchanging for gold.
Maybe the biggest problem though is maintenance. Houses sitting vacant in China are often poorly maintained, meaning that their book value is far higher than their actual value, so that assets currently valued at X are actually worth far less at Y, which alone is already a significant warning of a bubble.
So why are houses worth what they are? Because people hope that someday someone will need them. Gold has value for what it does today, whereas China's vacant homes serve no purpose today once built besides looking nice, and as such have value for what they'll hopefully do tomorrow. With a stagnant birthrate, a falling population, and increasingly unmaintained property, China doesn't offer much promise for these homes ever being useful for anything. The problem is that just as gold derives much of its value from its use as an alternative investment, investment options for the Chinese are fairly limited, with real estate the only major reliable investment available to middle-class Chinese offering decent returns.
This amounts to a fairly scary set of circumstances for Chinese citizens holding much of their wealth in real estate, especially those who plan on retiring in the next decade or so, with an already tenuous safety net due to the age distribution. If real estate falls, much of China's wealth falls with it, and the average citizen will be the first to suffer. I hope your skepticism stands correct, and there is no real estate bubble in China. I fear, however, that there almost certainly is.