RE: Strange enchilada sauce
Never. For the most part, there's not much of a place for vinegar in Mexican style cuisine because of how it dominates and subjugates the delicate flavors of the peppers and other ingredients. A good example is chunky salsa, or pico de gallo as it's known around here. It's served brilliantly fresh with fresh aqueezed lime juice as its acid, and the onions, chiles, tomato and cilantro are all raw. The nasty crap you buy in the store, like that Pace garbage that's so popular back east and in the mid-west, is not only cooked but it's preserved with so much vinegar as to nauseate.
If they're using vinegar they're hiding something.