Yes they invested enormously in high-speed train lines. But look on satellite image around those train stations, new city blocks have massive roads everywhere, 5 lanes in each direction, plus in parallel another set of toll roads. Even if those roads were empty , the cement and steel for all that has contributed enormous quantity of CO2 to the atmosphere.
Chinese emissions per capita are higher than european average for many years now, however they always pick the worst country in the world for comparison statistics.