Thats because the Class 1 CBSE books said that Hindi is our national language, Peacock is the national bird, Tiger the national animal and Hockey the national sport. :D
That's not entirely correct. Hindi is the official language of Republic of India. That is why 14 September is celebrated as Hindi Divas: https://en.wikipedia.org/wiki/Hindi_Divas
That is not entirely correct either. Hindi and English are official languages of the Republic of India. If you watched the swearing-in ceremony of the recent Modi government some cabinet members chose to be sworn-in in English.
