The Fields Medal is structured in such a way that it's awarded to people under 40, and this creates an interesting effect - it often becomes recognition not so much for a specific result, but for the potential and direction of a scientist's thinking. The fact that a Chinese mathematician received it suggests rather that a whole school of fundamental mathematics has grown up in the country, rather than just the solution of some single problem.
As for practical impact - in pure mathematics, results often manifest themselves decades later, in completely unexpected applications. Modern cryptography, machine learning, even engineering calculations often rely on theories that were developed without any thought to practical use. So increased competition in this field is generally good for science.
And the fact that China is now investing in fundamental research instead of waiting for Western scientists to come up with something - that's a long-term game. Resources, talent, access to the best minds are drawn to where there is recognition and opportunity. That's how the scientific world works.