Call it what you want. But the fact is that for several centuries, the language spoken in north-west India was called "Hindustani" - a fact that you did not know until now. This classification into urdu and hindi came much later. In short, don't get so worked up because you saw a wikipedia entry about "Hindustani", because yes, that is what it was called previously. A lot of north Indian classical music was also composed in "hindustani", and called as such. As you can see, encyclopedia britannica also has an entry about it, and as you know, EB is not crowd sourced. Maybe because Pakistanis have tried to erase history in schools, that you are not aware of it.
You were just plain wrong when you thought no such language ever existed. It did, and urdu and hindi are a recent diversification.