When Muslims came they adopted the language of Delhi. slowly they started adding Persian /Arabic words. further down, they even started imposing their own grammar rules. All this lead to the creation of two streams
A misconception about Khadi Boli is that it came from Braj bhasha but due to the influence of Muslims, it took a new form. However, this is false and Khadi Boli (KB) is as old as Braj and Awadhi. The only difference is that KB started producing literature much later than Braj.
Amir Khusro ( 1253-1325 ) was 1st prominent poet of KB. This is what he said about Hindi ( KB variety) when he encountered the language. This proves KB was already there by the time Muslims settled in Delhi. It's a 100% Hindu language discovered by Muslims, not the other way round.
Hindu poets were also using KB in their poetry. It was common practice to describe the conversations between Muslims in KB. So we can see that although there were other forms of Hindi such as Braj and Awadhi, Muslims mainly got associated with KB only. It's clear that poetry in KB is, if not older, at least as old as the time period of Khusro but it was not much respected in the world of literature. Prose writing in Hindi (not just KB) started in the 18th century. For prose writing, KB was adopted as the preferred variant.
One claim about KB, often made by secularists of the Ganga Jamuni variety is that Urdu is older than KB, and Kb was derived from it. This is untrue. Mohd. Kuli, considered to be the first Urdu poet is from the 17th century but we can see the existence of KB poetry even before 1300 CE.
Long before Mohd. Kuli, Urdu poetry had been influenced and impacted by Braja bhasha. Though later on, we see the Urdu poets abandoning Braja in favor of Persian words. That said, one cannot deny that KB grew in importance and reached wider geography due to Muslim patronage.
Urdu, which was born from and nurtured by Hindi started attempting to differentiate itself from the original Hindi as it started to mature. This distance was sought to be created through the continual increase of Arabic & Persian influence.
Over a period the distance between Hindi and Urdu grew and we can see 4 clear differences between Hindu and Urdu
We can conclude by reiterating the obvious fact that Hindi and Urdu are not the same. It's true that what we know as Urdu was born from Khadi Boli spoken around Delhi and most likely would not even have been recognized independently had it not actively sought to differentiate itself.
It was probably the arrogance of the ruling elite who thought the language of natives (Hindus) was not good enough for them(Muslims) and that's why they kept trying to distance Urdu from Hindi. This is the reason why Muslims, more than others, understand Urdu & Hindi are different.
This is why you see Urdu as the official language in states where Hindi is already is an official language. UP and Bihar are such examples. If Both Hindi and Urdu were the same Muslims would have been happy with Hindi alone. Why did they demand Urdu if Hindi was already there?
Why does the Muslim majority state of J&K not call its official language Hindi instead of Urdu? So we can see Muslims have no confusion about what is what. It's the Hindu who seemed to be confused although just by looking at the actions of Muslims they should have known that “ Hindi Urdu is same” or “ One language two scripts” is Bullshit. It's amazing how forgetful Hindus are. The Hindi Nagar movement clearly established not only the popularity and legitimacy of Hindi to be the official language but also its differences with Urdu is less than 150 years old and Hindi became the sole official language in UP only in 1947.
Greece was conquered by Islamic Ottoman Turks in the 15th century. After 300+ years, Greeks got their freedom. The first thing Greece did after Independence was to purge the Turkic & Arabic words that have entered Greek vocabulary. They created a standard Greek called Katharevousa. Indeed, Greece faced similar challenges that India does. An ancient Civilization. Subjected to the foreign Turkic yoke for 300+ years. But the similarity ends right there. Their respective reaction to colonization after independence was startlingly contradictory. When Greece became independent in 1830, there was a substantial Greek-speaking Muslim population within its boundaries. These Greek Muslims used to write Greek language using Arabic script. However, Greeks did recognize this as a separate language or confer it any official status. Instead, Greeks made Katharevousa (Greek without Turko-Arabic words) their official language. Anybody who did not comply was free to leave the country. In India, just the opposite happened. The adulterated Hindi with a foreign script was not only promoted as a distinct language.
Not only that, India's leaders like Nehru actively promoted the Hindustani language and almost went to confer it the official status. Today, Greece does not have a language problem.
Ioannis Kapodistrias was the first Governor of Independent Greece. He declared -“ If I write Turkish using a Greek script, will Ottomans recognize it as a distinct language? Greek will be written in Greece using only the Greek script. Every other script will have to be discarded”