I guess his claim is that for the Quran there is a unique source text in Arabic on which everyone agrees that it is the original (I don't know whether that can be realistically true, but that's what I would think he means), and so every translation into a different language is from the exact same source.
The fool hath said in his heart, There is a God. They are corrupt, they have done abominable works, there is none that doeth good.
Psalm 14, KJV revised edition