Whether it is one person's rehashing is another debate. We don't possess any original Quranic manuscripts, early manuscripts show changes, parts of the Quranic script was eaten by goats and current manuscripts vary in content, albeit in minor ways.
It's not to say that Mohammed didn't receive a correct revelation, that his followers didn't memorise it correctly and the first version of the Quran wasn't a perfect copy of Mohammed's revelations. It's just we don't have the original scripts to support this claim. And if we're going to subject the new testament to higher criticism then we need to do the same to the Quran.
It's worth reading tom Holland and Dan brubaker. Others will disagree, but from a historical perspective there is a lack of evidence for the perfect recording of a single author.