Islam in general refers to the religion which God Almighty sent His Prophets to teach mankind: The worship of the One God alone (pure Monotheism) while submitting to God's will in gratitude for being given life and innumerable blessings.
In addressing this misconception, it is interesting that no other religious scripture claims to be the direct word of Almighty in toto as clear and as often as the Holy Qur'an. As the Qur'an clearly says:
"if had been written by man, you would have found many discrepancies therein". (Qur'an 4:82)
At the time the Qur'an was revealed, the Arabs recognized that the language of the Qur'an was unique and that it was distinctly different from the language normally used by the Prophet Muhammad, peace be upon him. The Arabs of that time, by the way, were known for their beautiful poetry and Muhammad was known to be an illiterate man! The Qur'an clearly says that Muhammad was unable to read and write (Qur'an 7:157), so if this wasn't true, certainly his contemporaries would have protested and rejected him. However, there are no reports of this.
Certainly there were people who rejected Muhammad's message, just like other Prophets were rejected, but none for this reason. On the contrary, Muhammad, peace be upon him, had thousands of loyal followers and the results of their efforts spread Islam from Spain to China in just under a century! It is also interesting to note that even though the Qur'an is not poetry, the Arabs more or less gave up writing poetry after it was revealed. It could be said that the Qur'an is the piece of Arabic literature par execellance - and Muhammad's contemporaries realized that they couldn't out do it.
Additionally, it is easy to prove that Muhammad did not possess a great deal of the knowledge which is expounded in the Qur'an: such as knowledge of historical events, previous prophets and natural phenomenon. The Qur'an says in several places that Muhammad and his people did not know these things - so, again, if this wasn't true, certainly his contemporaries would have rejected his claims. Suffice it to say that not only is the Qur'an the most memorized and well preserved scripture on earth, it is also unequaled in eloquence, spiritual impact, clarity of message and the purity of its truth.