Yes, some confusion is probable, since there are, within 'libertarianism' today, many flavors of 'libertarian' who would point to different origins/sources when deriving their first principles. I would refer to myself as a 'Natural Law Libertarian," I suppose. 1) there is an external natural moral order to which we must confirm; 2) it is known in the hearts of men (though frequently repressed); 3) to go beyond the natural law is unjust at best and tyrannical at worst. So 'my people' are those at, say, the Mises Institute. The form of 'classical liberalism' I mean would be from Locke, from Mises (See his book, _Liberalism: In the Classical Tradition_). For some background on how these movements have morphed and been re-named (the term 'liberal' having been stolen by the progressives a hundred years ago), you might look at Justin Raimondo, _Recovering the American Right_, or Rothbard, _The Betrayal of the Right_, among plenty others. I know--it's rich for me ask you to read these books after I said I am not likely to read the one you suggested--granted. Time is short, and I have 100+ books already on my list, most already within my own tradition, and I probably won't get to them all before I die. Point is that after years of study and thinking, I've "found my people" both theologically and politically, and now I wish to spend my time going deeper into them. As a classical liberal I am opposed both practically and morally to any forms of involuntary collectivism (socialism, communism). I think anarchism gets a bad rap and, though I'm not quite willing to wear that patch, I am certainly drawn to it--by necessity of logic. This 'brand' of anarchism only means no overarching MAN as ruler--it does not preclude all authority whatsoever. "Sphere sovereignty" comes pretty close.

Even Murray Rothbard, who was at least an agnostic, realized and promoted the idea that without some transcendent lawgiver we have no ground for our first principles. See his 'Austrian Perspective on the History of Economic Thought' -- though he gets some basic details wrong in what we Reformed/Protestant believe, he's "directionally correct." I'm sure you've read MLK Jr's. "Letter from Birmingham Jail" that touches on some of the high points in Western history related to just vs unjust laws, and their sources.

I hope that at least approaches the question you're asking.