I think I've heard something similar -- that subjects have duties while citizens have rights.

But of course, citizens typically also have duties -- commonly, the duty to take up arms to defend the state -- and subjects can legitimately expect a reciprocity of obligations from the sovereign (e.g. the enforcement of the "King's Peace"), which sounds quite a bit like rights to me.

(All of which is a verbose and not very coherent way of saying that I agree with you.)