The shit smell could have been any kind of sulfur compound. Without sufficient nutrition, oxygen, and nitrogen, any remaining yeast will use available sulfur to make hydrogen sulfide. Plus, some yeasts are more prone to form sulfides than are others. Racking, topping up, filtering, and bottling allow the incorporation of oxygen and help to prevent sulfide formation. But the addition of elemental sulfur, either in the vineyard or to the wine, can do just the opposite.
They stink but do not “blow off” with aeration and they aren’t easily oxidized. They simply form disulfides or heavier, less volatile, sulfur compounds for which we have higher sensory thresholds.
On the other hand, the lighter sulfides can precipitate with a copper penny. (Little copper in US pennies these days, so use a piece of wire or something.)
Some people don’t think that a little stink is a flaw and in fact, sulfur compounds aren’t always unpleasant - the yeasty or bread-like aromas from aging on lees that one might detect in chardonnay or sparkling wine is also a reductive scent, and the petrol scent of riesling is another, and what I think people sometimes call “mineral” notes in highly acidic whites may be yet another.
Brett is different.
First, it’s all around. So if your winery isn’t clean, you probably have bretty wines. This was characteristic of many French, Italian, and Spanish wines in prior years.
Second, with a little oxygen and nutrients, Brettanomyces of some strain or another can grow using the alcohol in the wine as a source of carbon, some amino acids in the wine for nitrogen, and even some of the sugars in the wood of the barrels, particularly the toasted woods. Thus the wine needs to be able to eat up, or use any available oxygen, so as to deprive the Brett of any ability to grow. Also, it grows quickly at temperatures above 60 degrees F, so keeping the wine cold is important.
Still, higher pH wines (lower acidity), higher sugar levels, and in some cases, reduced use of sulfur (“natural wine”), all contribute to the growth of brett. So even if your winery is clean, your winemaking style may contribute to brettiness in your wine.
I think you had something other than brett. Probably brett too.