Is Bhutan India's De Facto Bassal State?

Daniel Nicholson says Bhutan is India's de facto Bassal state. If not how invited India go on to become the security guarantor of Bhutan. Could PRC be possible of China choose Bhutan to be its battle theerer in a short war with India? A Bassal state is a state that is used against its will to play various kinds of roles for superior power.