S-400 long range capability is mostly theoretical, as there's no stock of the 40N6 missile capable of it. Especially doubtful in case of China, given the secondary nature of their missile technology.
China builds their own interceptors so the availability of Russian stockpiles isn't relevant, they've both deployed and conducted real world tests on multiple interceptors beyond the initial 200 KM range that the system went into service with including having improved interceptors that can counter ballistic missiles and satellites[https://en.wikipedia.org/wiki/2007_Chinese_anti-satellite_mi...].
By all accounts it was a modified HQ-9 interceptor which was piggybacked on a short/medium range ballistic missile (mostly because of the high inclination of the test satellite, which might mean it's quite likely to be potentially capable of reaching LEO VISINT satellites which pass over the interceptor on it's own).
Any space faring nation has technology to intercept LEO satellites. That doesn't mean a tricked out ICBM has any use in intercepting manuvering fighter jet.
The original HQ-9 interceptor is stated to have 200km slant range, just as the Russian missile it was faithfully copied from.
The ICBM didn't hit the missile the HQ-19 interceptor did, and no not every space capable nation can shoot down a satellite look how many decades it took the US to being able to do achieve that.
Most SAM's have different profiles and interceptors that cover targets with different capabilities this quite often limits their range, you can argue about the exact range and operational ceiling for the interceptors in question all day long it still doesn't change the fact that China has deployed one of the most sophisticated SAM's currently in operation on and island that they might not have full legal claim for which can threaten quite a big chunk of the air traffic over the south china sea.