Western Europe, through the British conquest of the subcontinent, was woefully unaware of the internal differences. That Columbus ill-advisedly thought of India as a monolithic entity is no marker of anything.
The language thing sure does. But the only time in ancient history Western Mediterranean Europe has been part of a single state was during the Roman period. the rest of the time they evolved separately and uniquely. In contrast each part of modern India has been politically linked to the other parts multiple times through history resulting in a common culture but with some obvious diversity. E.g. Indian festivals are largely common throughout the country, a marker of commonality stretching back through history.
>> That Columbus ill-advisedly thought of India as a monolithic entity is no marker of anything.
He said nothing about it being monolithic, just that there was a place called India, and it was worth a visit.
Your original comment was "there was no 'India' ...".
There has been an India through most of history. But of course the borders of the modern state were drawn relatively recently. These are two different things.
The original point was "there really was no 'India' before the British cobbled one together". If so, then where was Columbus trying to go? Of course there was 'an India', it just wasn't structured like a modern nation state, which is true for every other modern country as well.