In this context, the Copernican revolution is Kant shifting the human away from the centre, in the same way that Copernicus shifted the Earth from its former position at the centre of the universe with the sun revolving around it. The previous revolution is known as the Cartesian revolution, after Descartes' famous Cogito ergo sum ('I think therefore I am') placed the human mind and experience at the centre of philosophical inquiry.
This relates to the thesis of Northrop's The Meeting of East and West. He claims that a major difference between Oriental and Occidental philosophies is the absence and presence of the subject/object division respectively. It is easily seen in the Western cliché of Oriental 'One-ness', where a person can be 'one' with something other than themselves, an idea which is not commonly found in the West. This idea is further manifested in Buddhist ideas of non-reaction and experience rather than intellectualising experience.