Short version: A few ultra-rich people in the US own a lot of real estate, bringing up the average, whereas in china its more equally spread out.

When the mean is very different from the median, it means the standard deviation is very high (IE, the values are really spread out, rather that clumped close). A simple example would be 2 economies each with 3 people.

Economy A: 1 person owns everything (Lets say $100 bucks), the 2 others own nothing. Average: $33, Median: $0..

Economy B: Each person owns $33. Average: $33, Median: $33.

The gini coefficient refers to the same thing, but measuring inequality within an economy specifically: 0 gini means everyone has the same net worth, 1 gini means 1 person has 100% of the value. In capitalism, the end-result is just like in a game of monopoly: the end result will be 1. In socialism, the end result, acheived via planning an equitable distribution, should be to get as close to zero as possible.

As the other response pointed out, this graph obviously hints at greater wealth disparity in the US vs China, as one of the most common ways in which the mean can be pulled upwards relative to the median is by the presence of a small minority with extreme wealth at the very top. The median while not perfect is a better representative of the situation in which the "average" person finds themselves, as by definition half are above and half are below this value. Imo one of the most important statistics concepts that everyone should learn is the difference between mean and median and what each value can tell us about how a set of values is distributed.