Pi's full first name is Piscine, and at school, everyone made fun of him because it sounds like "pissing". But at that time he was in India, and "pissing" is an English word. The actors spoke English because it's an American movie, but the characters would've really been speaking Indian.
Arrant nonsense. Puducherry was, is & probably will remain predominantly Tamil speaking. There's no such language as "Indian". The closest to national languages in the current post independence nation of India are...Hindi &.... English. Even in a former French enclave like Pondicherry/Puducherry.
In fact, so pervasive is the English language that all students learn the language from an early age as a matter of course. Additionally, all major national & major metropolitan editions of daily newspapers have English language editions. The average educated Indian citizen would have a far superior command of the language (at least in terms of the basics of spelling, syntax & vocabulary) than his or her North American counterpart. The connection between English & indigenous languages of the subcontinent has been so ubiquitous & pervasive and of sufficient duration for there to exist extensive cross-infusions of vocabulary between them. Including Pi's pejorative nickname.
PI said he had French courses, not English ones. So they were clearly impregnated with French culture first. And these kids would already know English instead ? I doubt it.