It is likely not bad. I made the same mistaken assumption on my first attempt at cider this year. When most of the sugar is taken out of the cider and you have the dry, alcohol, apply flavor, it bears a resemblance in flavor to mild vinegar. I had a BJCP national judge I know come over and check mine out because I thought the same thing at first, and I had done multiple batches with different cider blends in each.
Once I back sweetened them a bit they were quite tasty. You do want to keep your oxygen exposure to a minimum on cider as it can go to vinegar with oxygen and acetobacter.
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