There's almost certainly wild yeast on the grapes themselves; and in any case yeast is more or less omnipresent, so you'll have wild yeast all over your own kitchen at home. The usual problem is preventing things from fermenting, not causing them to ferment.

I doubt those “subtle things” were a priority in this case. Or any consideration at all. People didn’t drink this stuff for its flavor.

Not much has changed if you look at the cheap alcohol available.

Even cheap alcohol is much much better than it used to be. Mulled wine was so popular back in the day because wine was barely drinkable. Cocktails exist for the same reason (and that’s why classic recipes are so sweet). It’s a similar thing with classic “ethnic” dishes—they are so rich and flavorful because they needed to cover the taste of marginal meat.