That is what Wikipedia says about the Quran. Since the Quran is the perfect word of God, why are there many Muslim faiths? This problem interested me for a long time, but it's only now that it occurred to me that there may be a simple answer someone else knows.
As an atheist I'm hardly an expert, but it's been explained to me that the disagreements between the Sunni and Shia Muslims concern things that happened after the Quran was transcribed. Worldly things, like who deserves to be in charge.
The Quran is not the entirety of Islam. The Hadith are considered to be equally valid, but not every sect accepts every version.