The bombards (muzzle loaded cannons) were widely known and used in Europe, e.g. the famous Mons Meg (https://en.wikipedia.org/wiki/Mons_Meg); what distinguishes the cannons that Mehmet had Orban built (https://en.wikipedia.org/wiki/Orban) were their sheer size and the technological knowledge in casting such massive bronze bombards, that Western Europe lacked at that time. For an informal description of Orban's work see http://www.camrea.org/2017/09/11/orban-the-man-who-brought-d...
Note that just having this massive cannon did not make it a done deal: due to overheating, the bombard had to be cooled for a long period after each shot in which time the Byzantine defenders quickly mended the walls with rubble and any other materials they could find. In the end they just got overwhelmed.
Constantinople would likely have fallen anyways, it was just a matter of how long it would have taken and how many lives would have been lost.
This is Turkey's official rhetoric, but hardly the general truth. In today's Turkey, and in the Ottoman Empire, the only thing that was really Central Asian was the Turkish language. The reality is that most possibly the Turkification of Asia Minor was a case of "elite dominance", as allowed by the gap of historical knowledge in the region for many centuries during the Middle Ages and as backed by contemporaneous genetical studies (which relate the local population to Mediterraneans rather than Central Asians).
The fact is lots of pseudo science was involved in building a Turkish identity decoupled from Islam during the process of the establisment of the modern Turkish Republic. That's not unlike the similar and similarly funny stories some Hungarians entertain these days, and based mostly on linguistic relations. The Central Asian Turks migrated, thoroughout decades and centuries, westwards, and firstly became Persianised and Islamised, and then became the Muslim warrior elite, and then they built multiple states during some centuries around and in Asia minor, and they begat ultimately the Ottoman Empire, and the peoples were Turkified; but the only concrete thing that change were the lords. At least, this is what genetical data suggests (Arnaiz-Villena et al. 2001, Hodoğlugil, and Yardumian are some examples).
I take an issue with this narrative as a Turk because that's a fundamental lie the current national identity that we sport is based on, which renders it unsound.
> It took another 700 years and Mehmet's use of cannon to bring the walls down and really change history.
That's debated too. But cannons or not, what remained for him to conquer was the crumbs of the empire, fitted into a city which you can walk across in both axes with slow tempo in a bit more than an hour. The west left them alone, and the 4th crusade had already rendered them terminally moribund. It's indeed fascinating that he declared himself the new Emperor of Rome, but it's still so w/o the mythology.