Well, you heard it wrong.
It didn’t "fall". There's a different story on how Quran came into being.
Quran is a book of revelation… rather like the Bible.
The basic story is this…
Quran (or the texts inside it) was orally revealed to Muhammad, the last prophet, by God, through an archangel Gabriel. As Muhammad was revealed Quran, he and his few companions would record it in writings. This continued for 23 years, from the time the Prophet was 40 years old till the time he died.
So, Quran didn’t really "fall". It was revealed over a very long period of 23 years.
Once Mohammad died, all these revelations were jotted down together by his companies and followers. A complete Quran was compiled then.
Of course, there are many layers to this answer. A lot happened in these 23 years. Many major events took place that went on to define Islam and establish Mohammad as the messenger of God.
(Courtesy: Egypt Today)
But in simple words, this is how Quran came into being.And soon, with stories of Muhammad spreading through a new religion that had everyone's attention back then, Quran spread too. And it soon became a book of guidance for mankind, (blindly) revered by Muslims around the world.
Hope this answers your question.