The buttermilk is acidic enough that it interferes with the environment that commercial yeast needs to reproduce well
I don't think this is the case. Yeast prefers a mildly to moderately acidic environment: pH 4.5 - 6 (7 is neutral). The various sources I've found give a pH of 4.1 - 5 for straight buttermilk, and of course that pH is buffered (brought closer to neutral) when you mix it into your dough with the other ingredients. If anything, I'd say that a buttermilk dough would be ideal for yeast growth, provided there's enough water available.
The key difference between baking soda and baking powder is that soda is just the alkali, where baking powder is a mixture of baking soda and a powdered acid, usually tartaric or citric.
You can use baking soda alone with a buttermilk dough because the buttermilk provides the required acid component. For buttermilk pancakes, I like to use a combination of baking power, plus a bit extra soda: Think of it as if the powder reacts with itself, and the soda reacts with the buttermilk (although it's not really separated like that).
So, really any or all of those agents can make a buttermilk loaf rise. The important thing, I think, is that yeast and baking powder/soda have very different effects: not all rises are equal! Powder/soda reacts as soon as its wet, and then again when it gets hot in the oven. It creates bubbles, and that's about it.
Yeast does much more besides. As it ferments the dough it also creates a complex mix of enzymes, sugars, acids and alcohols which affect the flavour, structure and baking characteristics of the bread. The protein structure of the flour changes, and that has a big effect on the finished loaf.
Buttermilk also has some amount of fat in it, which has an effect on bread dough. The fat tends to coat the flour particles, which results in shorter gluten chains - this gives a softer crumb with smaller holes: think brioche vs. ciabatta. You might want to knead or fold your dough more than you would otherwise to compensate for this effect (depending on what you want). My hunch is this is what caught the original author out, not the acidity.
If you're making a typical 'bread', I would just use yeast. The buttermilk will contribute flavour and sourness, and give that texture change I mentioned. If you're just after the tang, a zero-fat natural yoghurt would provide a very similar flavour while affecting texture less.
Unless you're making Irish soda bread (and you should, it's delicious!), I wouldn't bother with powder/soda raising for bread. Yeast does too good a job - save the powder for cakes and muffins!