Your basic description of the eavesdropping of jinn and their passing information on to fortune tellers is correct, based on the Qur’an and prophetic reports.
This phenomenon occurred much before the coming of the final Prophet Muhammad (peace and blessings be upon him), although when passed down among the jinn to earth and eventually to astrologers and fortune tellers, the information they heard would be mixed with hundreds of lies.
Yet with the coming of our blessed Prophet (peace and blessings be upon him), the “stations” from which they would listen were found guarded by angels. Moreover, when they still attempted to listen in, they would be pelted by piercing flames (shihab). When they tried to investigate the matter, they came to know that the new prophet had arrived in the Arabian peninsula.
Allah cast out the jinn with piercing flames to end that phase of eavesdropping, with the exception of “stealth hearing” by a few jinn, who are then kicked out and pursued with flames.
“We have surely placed constellations in the heavens, and We have adorned them for those who gaze and ponder. And We have guarded them from every devil cast out; except for any who hears in stealth, and is then pursued by a clear flame.” (15:16-18)
“Verily, We have adorned the lowest heaven with the adornment of stars; and [We have placed] a formidable protection from every obstinate devil. They cannot listen to the Highest Realm, and they are pelted from every side. Outcast!—and theirs is a perpetual torment—Except for one who quickly snatches away [some information], after which he is pursued by a fiery flame.” (37:6-10)
“And indeed, we seek out the sky [i.e., the information there], yet find it filled with fierce guards and flames. Yet we used to sit there in stations, so as to hear. But any who listens now will find flames awaiting him.” (72:8-9)
There is actually a section in Sahih Bukhari, in the Book of Tafsir, entitled, “His statement, ‘Except for any who hears in stealth, and is then pursued by a clear flame.’” (15:18)
The hadith in that section describes how the jinn climb one on top of the other [according to the narrator, like one hand over another] to the heavens, where Allah decrees a matter in the presence of angels. A jinn will hear some information in stealth, and if not burned by a flame, passes it down below, one after another until it reaches earth. It is finally given to the mouth of a sorcerer, who conveys it mixed with a hundred lies. If anything proves true, people will say, “Didn’t he tell us on such-and-such day that such-and-such would occur, and we found it to be true?”
Reconciling This with the Verses You Ask About
Allah Most High says in the Qur’an, “[He alone is] Knower of the unseen (ghayb); so He allows no one access to His unseen. Except to a messenger whom He has chosen, and then He makes a guard to march before him and behind him.” (72:26-27)
There are a few ways of reconciling these verses with the the phenomenon described above, of Allah disclosing information of the future to angels:
(1) As you state in your question, some exegetes do mention that what is meant by “no one” is “no one among mankind.” [Tafsir Jalalayn]
(2) Even if this were interpreted as “no one among creation,” it does not necessarily contradict the aforementioned phenomenon. As explained in detail by Imam Razi, this is because the phrase “His unseen” used in the verse has no indication of generality. It does not necessarily mean “all of His unseen.” Rather, it could mean “part of His unseen.” [Mafatih al-Ghayb]
That is to say, there are some things in the unseen realm that Allah Most High does not disclose to anyone, except to chosen and elite messengers. This information includes both revelation (like the Qur’an sent to our Blessed Prophet) as well as future events: it is not disclosed to angels in the Upper Realm, and jinn cannot eavesdrop to hear it, even in stealth. As the verses mention, there is even a guard of angels, in front of it and behind it, to provide further protection from evil jinn.
Yet this information is not all of the unseen, and so there are other things of the unseen that Allah does disclose to angels of the upper realm, which jinn can then listen to in stealth.
(3) Imam Abu Su’ud mentions in his tafsir that what Allah prevents to creation is “complete access, whereby there is full disclosure of reality, allowing for full certainty”…except to elite chosen messengers, who are given a “partial disclosure of the unseen,” i.e., specifically that which pertains to their message, such as miracles to prove their truthfulness, or rulings of law and morality that people must abide by; as well as states of the next life, such as resurrection and judgment…namely, those things of the unseen that are part of the prophetic duty to convey. [Irshad al-Aql al-Salim]
Hence based on this interpretation, what is barred from creation is full disclosure: this does not negate that certain events of the future can be disclosed to angels, as well as evil jinn and hence fortune tellers (albeit mixed with many lies)…
And Allah knows best.