The biggest problem with one rather monocultural kind of Pakistanis looking at India who haven't been in India is that they can't imagine what it's like in daily life in any major city. They can, and do visualise pretty well what happens in towns, the smaller ones, especially. That should prove something or the other, just at the moment I can't be bothered to tease out the details.
You might also like to instruct him on the antecedents of the Sylheti dialect, and why it has less to do with Urdu, more to do with its linguistic descent and environment. But that would never penetrate to his bigoted brain.