I sometimes get sidetracked by questions like I put in the headline, partially because I have ADD since I was little, and something that might be related to that, I have an insatiable curiosity about, well EVERYTHING!
Now usually a trip to the library or a quick Google search answers my curiosity, because we humans have answered most of the easy questions. But in this case, the answer is not-so-easy. Acetobacter have been found in the wild, but are they wild or just escaped from humans? My google-fu says probably wild and evolved because yeasts sometimes ferment flower nectars into alcohols and wherever there’s a food source there will be something evolved to eat it. So the conclusion is Acetobacter predates human evolution, and was not the result of leaving beer uncovered in Sumeria after brewing.
Also there are very many varieties of Acetobacter in the wild, which also suggests that vinegar is not the result of humans leaving their wine and beer uncovered. So far the evidence we have is that beer and wine pre-date writing by about 1K years, as pottery shards have been found with residue from beer and wine that predate the earliest known writings. And there have been Acetobacter around long before that, meaning there has been malt vinegar around millennia before there were fish and chips to put it on.
So, this is how my mind works.