Yes, 'Sanju' is a true story. It attempts to depict the highs and lows of Sanjay Dutt's life with as much authenticity as possible. But keep in mind that in the process of adapting a real life to the big screen, some elements might be dramatized or simplified.
The good explainer stories are those that can clearly convey complex ideas or information in an engaging way. For example, fables often use simple characters and plots to teach moral lessons.
The truth is, it's hard to say for sure. While it might have roots in reality, the story could have been modified and fictionalized to a certain extent to create a compelling narrative.
Aesop's Fables are great explainer stories. For example, 'The Boy Who Cried Wolf' is used to teach the importance of honesty. It shows how lying can lead to a loss of trust.