Would you be able to show a picture of what you're talking about?

Oh, yeah. I took tons of photos of those walls over the years. Most of them are in archives, though; like I said, we lived there over a decade ago, but I have one in my front photo album:

I do have a picture of one end pillar, but that has pointing, and it's not obvious that pointing is aesthetic and not structural mortar (although it is often applied over mortered stone). Anyway, you can't tell the stone isn't mortared b/c of the pointing, so it isn't a useful illustration.

That photo above, however, is clear there's no mortar, and yet that hundred y/o wall is astonishingly straight and level.