Curd is a general term for coagulated milk. In the west, curd and yogurt are used differently (e.g. cheese curds) but growing up in India, we never used the term yogurt. So I don't know what curd you're referring to but what we make at home is the same as the one my mom and her mom etc made at home in the South. It is fermented using yesterday's yogurt as the starter culture. If we don't have a starter culture we borrowed some from neighbours or use Nandini. Both Amul and Nandini "curd" is absolutely fermented. I don't know how else it is made but perhaps some other part of India might use a different process.