He's not right.

If you discount China as a superpower, then you discount a country that could single-handedly throw the entire world into a state of political, economic, and military chaos overnight.

Defining power as military-only is as naîve as defining it as male-only or violence-only or sword-only.

You are right. One should take care defining a word so narrowly that it can only apply to one thing. If "superpower" by definition means "characteristics only the USA has" then why not just call it "USA?"