This comment reflects in many ways important elements about how and why the Chinese view the Indians as they do:
… your question has answers in two periods. The second and most recent was during the cold war, shaped by Chinese elite (diplomatic) interaction with their Indian counterparts during this period who came to see Indians as unserious prevaricators. Big talkers and little doers, whether or not you agree with this assumption, it is what drives Chinese elite opinion today.
The first and older break was an earlier schism in worldview at the dawn of the 20th century when Chinese elites chose to take the path of Darwinian materialism towards national salvation. This meant radical politics and a restructuring of Chinese society towards any ends at any cost as long as it meant material prosperity and power. This left China lurching between fascism and communism. At the same time they came to view simultaneous Indian political trends, another vast nation under Western power, as being embodied by Tagore and Gandhi. That is focused towards traditionalism and eastern metaphysics as a path to revival. This is again may or may not be true but it became the default opinion. This was actually shared by elements of the Chinese elites as well, though the losing faction. The winners of the debate viewed such a policy as childish escapism verging on nihilistic passivity in the face of real threats and India, as the eidolon of such defeated views became tarred by association.
As I have noted before, Adam K. Webb’s Beyond the Global Culture War highlights attempts by early 20th century Asian traditionalists to coordinate. Some of the same characters appear in Mark Sedgwick’s Against the Modern World: Traditionalism and the Secret Intellectual History of the Twentieth Century. For all the influence of Fabian socialism on Nehru and the early leaders of India, nothing on the scale of what happened in China to the traditional society occurred in India.
But today as many Chinese transition to post-materialism they are looking back to their own past. This is natural. But the past destroyed is not so easy to access and rebuild.
Addendum: Chinese liberals and progressives of the early 20th century adopted and modified racial theory from Europeans.