Is machine learning prerequisite to learn NLP?

Machine Learning is definitely not a prerequisite to learn NLP. But you will need Machine Learning to use NLP efficiently.

Your question arises from the fact that AI has been shrunk in the past few years. That happened because of those snake oil salesmen in the AI industry. Mostly the academicians. They made students believe that ML and Artificial Intelligence are the same. Because teaching ML is easier compared to AI – which is a vast subject.