No, acid doesn't "cook", cooking is heating to a certain temperature, acid doesn't do that. Also, our stomachs produce small quantities of acid, and only in the right and proper amounts for each meal.
What acid does do is generate the maillard reaction, which also occurs during cooking. But a lot of other chemical reactions happen during cooking that don't happen from acid, and vice-versa.
If you take a piece of meat and marinate it in any strong acid, such as lemon juice, you will generate this reaction, and it may have a similar color to cooked meat, but it's not cooked, and if you try to eat it, you will notice this difference. Or, if you put it under a microscope, you'll find all sorts of things different in both.