> it appears some other force of history in their culture annihalated all evidence of an technologically advanced civilization

There have been multiple occasions both in the imperial eras and the Cultural Revolution when the upcoming Chinese power has attempted to eradicate all evidence of a previous power that didn't fit an approved narrative. In particular, the "treasure fleets" were the victim of domestic power struggles.

The Japanese invasion of China was enabled by China's internal collapse and the final demise of the Empire. https://en.wikipedia.org/wiki/Empress_Dowager_Cixi