The reason is: China still have relatively few cars in terms of cars/capita. Looking at accidents/capica is really meanless (if your country with 1 billion people but has only one car, even if this car kills 100 people every day, you will still be ranked very low, LOL).
If you look at the accidents/automobile (this really should be the criterium for automobile safety), then:
US: 15.
China: 36, more than twice as much as US value.