OK, now that one is correct. Fermenting grapes let off gas, and that gas could explode the container it's in. The people had grape juice, grape ferment, and grape vinegar. They couldn't stop the juice from fermenting, so the wine went through all three stages. To avoid an explosion, the wine would have to be either fresh grape juice or vinegar - the final stage, otherwsie the flask would blow open.
But still. That’s wine in the process of becoming the kind of wine we know today. If being alcohol was bad, they would toss it out, not try to preserve it, unless there was a need for the vinegar.