The reality is otherwise. It was drafted by a bureaucrat called BN Rau. https://en.wikipedia.org/wiki/B._N._Rau

This really goes to the heart of what casteism is all about in a modern urban "casteless" setting. Any time a lower caste does anything of significance, upper caste detractors show up to tell everyone that the good stuff was actually the work of someone else of upper castes. The lower caste made his mark only through affirmative action or other kinds of "trickery". The constitution was obviously written by several people and the team was led by Ambedkar. You can use the same website- wikipedia- to inform yourself of Ambedkars contributions to society in general and the constitution in particular. Go and pick up a book written by him too if you have the time.

One of the nastier pieces of "information " about Ambedkar that an upper caste kid shared with me as a child was that Ambedkar was actually the bastard child of a Brahmin with a lower caste woman. This explains why he was so smart as all lower castes have very low IQ.