What we now call "India" is a totally artificial country that was created by a British multinational corporation in the 19th century. It includes hundreds of different groups who for most of recorded history were never ruled by the same government. With that being said, most Indians are indeed racially and culturally similar, analogous to how all Europeans from Portugal to Russia share racial and cultural similarities (as well as significant differences). The real outliers in the Indian context are peoples on the periphery of the subcontinent. For example, the people in the far northeast of India are mostly Mongoloids who are much more similar to Tibetans and Burmese than to your typical Indian. Those people often face racial discrimination from "mainland" Indians.