Yep.
What is unclear about that? “A set of two boxes” and “a single box” are not things that are considered equally serviceable from the point of view of the actor, so they are different goods (or rather, units of two different goods). I take it you are alluding to the view of David Friedman on the Law of DMU, as he explained it in the recent thread on it?
I’d be interested to hear whether David Friedman considers any of Hoppe’s statements in the OP to be a priori true.