What's the difference in benefits between apple cider vinegar and distilled vinegar? Presumably that's what the person was shooting for.
It's probably not for the main component (other than water) in all vinegar, i.e. acetic acid. It certainly can't be for its acidity, because in making the soap extra lye would have to be used to neutralize the acid. The alkalinity of the soap would wind up the same.
It's probably not for the sodium acetate that would form from this neutraliz'n. Technically sodium acetate is a "soap" the way chemists use the term these days. Acetic acid is a fatty acid although it's sure not very fatty, so its salt is a soap. But I've been told that all such short chain carboxylates do in soaps is act as an irritant. But maybe that's wrong; maybe along with the irrit'n, the skin is benefited somehow, the way urea softens skin and makes it itch.
But let's say it's not that. ACV has minor components that other vinegars don't. What those components are, I don't know, but they must be what people who specify ACV rather than just vinegar are interested in. Something from apple that's been worked over first by the yeast and then by bacteria. Could be all sorts of interesting minor stuff in that, and presumably somebody noticed it does something. Whether it works in soap, I don't know either.
