There's some truth to this. The Japanese preserved certain Tang Dynasty customs which were lost to China, and they have some of the best collections of Tang-era artifacts.
This line of thought was, however, used in very unfortunate WWII-era propaganda, like "we have to invade China to rescue its civilization, only we can do this!"
I'd argue its difficult to find major aspects of Japanese culture that don't trace back to ancient China (maybe the language, eating raw food and sumo)