The core of Hinduism remains the vedas, gita, the puranas and the upanishads. They lay out a very deep philosophy that theologians much more educated than I am have been investigating for centuries. It is a highly rigid system at its core (contrary to the freewheeling morass image Indians themselves have projected to appear non religious).
This is why India is a nation. From the tip of Jammu till the edge of Kanyakumari, people thought of the vedas as the progenitor scripture of all civilisation. They heard the exact same stories of the Mahabharatha and Ramayana for millennia. The fact that they were free to adapt it and retell or embellish it does not mean they broke away from the system itself or that the system emerged later than the stories did.
nation is defined as:
na•tion n. A relatively large group of people organized under a single, usually independent government; a country. n. The territory occupied by such a group of people.
That is a bad and definitely wrong definition
By my estimation India is an empire, and nationalism makes no sense in its context. Patriotism maybe, or political loyalty.
Just seems like a weird choice of political propaganda. I do understand there's a strong anti-Muslim attitude in India, which might be what they're calling nationalism. But it doesn't seem right.