Imperialism does but not the adjective 'imperial' which simply implies relation to an empire. Imperial Japan has nothing to do with the British and yet it is 'imperial'.
Any reader searching this phrase online or looking up any common reference will find the British relation. Unfortunate, but that is how it is. As an Indian, I have always known that. That is why the phrase jumped at me.
Is it too much to expect an author writing such a detailed article from this region to know that?
Even a paragraph later the emperor Asoka is mentioned explicitly