It's impressive how many high-speed railway lines China has built, but comparing countries without also taking their total area into account doesn't make any sense. Naturally, smaller countries don't have the need to build 50,000km of high-speed railway lines.

If we just divide the total length of the high-speed railway by the total area of a country, we get the following data:

China: 5.25m of high-speed railway / km²
Spain: 7.85m / km²
France: 5.56m / km²
And I'm too lazy to calculate the rest

Of course, China has large desert areas without any significant population (thus no need for a highspeed railway there), so a metric relying only on the total area is not flawless as well.