Your explanation of what happened is human speech, Nataq, in Arabic. This is the word used in 53:3. Thus, when prophet explained and provided details about his first-ever encounter with angel Gabriel, people started labeling him: he lost his mind, he erred, he is confused, perplexed, his desires are not fulfilled, he is frustrated, etc. 53:2-3 are comprehensively addressing all such labels. 53:4 is simply referring back to this speech/explanation/details of prophet including verses revealed if any, and stating, it is indeed Wahi, revelation. The word “huwa” in 53:4 is clearly referring back to the speech of the exalted prophet. Quran or Book are nowhere found in these verses. Thus, undoubtedly, 53:4 is not referring to the verses of Quran only. This is further strengthened when God clearly states in 53:10 – he revealed to His servant what he revealed. Thus, in this first-ever extraordinary encounter, angel Gabriel not only revealed some verses of the Quran, he also revealed what is Eman, who is God, who is angel Gabriel etc. etc. All such things are covered in 53:10.
53:1 Witness are the Stars that set along a course appointed. [They never misguide you. He Who commands them, commands the Messenger 6:98, 56:75. Wa = And = Consider = Witness = For = By. Najm is singular as well as plural in the form of a galaxy]
53:2 Your honored companion is neither in error, nor is he misled.
53:3 Nor does he utter the Word out of his desire.
53:4 This (Qur’an) is but a revelation that is being revealed to him.
53:5 He has been taught by the One Mighty in Powers.
Where does it say this is the revelation after the first encounter? Nowhere.
The Messenger narrated, spoke, uttered, the Words of the Quran using his own tongue, so NATAQ applies to this, not his own speech relating to the first encounter, once upon a time I met Gabriel whilst in a cave.
53:2 says he was not in error nor misleading the people and he could only do this if he had revelation from Allah, not his own speech/words.
53:3 clearly states that the Messenger was not repeating his own words, so was not recalling the first encounter which others did not believe so needed these verses to clear him of their charges.
53:4 says ‘this’ is revelation from Allah, so again running with the previous verse which are only speaking about the Quran.
When we get to 53:10, there can be no other explanation other than the Word the Messenger spoke was the Quran.
53:10 And thus He revealed to His servant what He revealed.
If the Messenger had received revelation not mentioned in the Quran, then was this so unimportant it need not go in the Quran? You say it was important as he received articles of faith from Gabriel, but this makes no sense. All such things on Eman etc are not covered in 53:10 as NONE OF THEM ARE MENTIONED THERE, this is idle, dangerous speculation to deceive the masses into believing in things not in the Quran and giving them the authority of Allah or the Messenger!
“creed of Ibrahim, the exalted prophet, and the Quran.” Is the same as following Quran with hadith, the hadith being fake news.