This may seem like a strange question at first, since well, we can literally see that the Qur'an is a book:
And we often refer to it as a book. And the Qur'an refers to itself as a book (Qur'an 5:15: "...There has come to you from Allah a light and a clear Book."). However, it doesn't seem that straightforward:
القرآن al-Qurʾān means "the recitation" (Wikipedia), which suggests the sequence of words in the Qur'an is what makes it the Qur'an, not the medium on which it's written,
the Qur'an was transmitted through "oral memorization and recitation" (see: Prophet Muhammad SAW was illiterate, who wrote the Quran then?), i.e., the Qur'an existed before it was in book format, and
I have the Qur'an on my computer in pdf format; we don't likewise call the Qur'an e.g. the "holy pdf" of Islam.
Question: Is it technically correct to refer to the Qur'an as a book?
This is a bit of a philosophical question: identifying the essence of the Qur'an, that which if we took it away, we would no longer have a Qur'an.
Update (or: what I've learned since I first posted this question):
Another question highlights that the word kitab (کتاب), which means "book", is used in Qur'an 2:2 to refer to itself The 2nd verse of Baqarah say: "this is the book", But wasn't the Quran sent down as a "revelation"?
III-AK-III writes the Qur'an did not, does not, and will not rely on manuscripts in an answer to The Birmingham Quran versus the present-day Quran This answer quotes the ayah:
Rather, the Qur'an is distinct verses [preserved] within the breasts of those who have been given knowledge. And none reject Our verses except the wrongdoers.
Wikipedia writes: When referring to the physical bound volume, some use the term mus'haf (مصحف).