I don't think so. Omniscient means "all knowing." That means the omni narrator knows what every character is thinking, feeling, etc. The omni narrator even knows what no character in the story knows (hence, all-knowing).
There are variations in omniscient vision. In the early days, the Greeks had the Gods descend onto the stage, to deliver pronouncements (the ultimate author intrusion), but authors have expanded it over time.
Just as I create individual narrators who have a particular insight or perspective (and a distinct 'voice' they use when describing incidents), some 3rd person Omni narrators know more than others. Just as the Greeks went overboard with God's speaking for the scriptwriter onstage, many authors prefer decidedly less 'godlike' narrators, who sound informal and personal, rather than detached and overly formal.
Again, the issue isn't that King used the 'I later learned' technique, it's that it came entirely out of left field. If he'd set the stage for it properly, no one would have questioned his using it. Simply starting with the story with a couple paragraph: "Looking back at my life, I've decided that ..." passage sets the stage for whatever comes later, when they later reveal what they had no right to know at the time.
My issues isn't with King for using that technique, merely for his being too damn lazy to use it appropriately.
Again, to use it properly, you need to establish the main character as a 1st-person omni narrator, even if he doesn't fit into that role for the majority of the story. But you don't just switch from 1st-person limited to 3rd-person Omni at the drop of a hat and not expect some significant grief over it.
Despite writing almost entirely in 3rd-Omni, I've NEVER had a 'godlike' narrator. My last posted story has the aliens who created the dilemma the character faced telling the story, but even their perspective was limited. It was more knowing than the MC's, but it was flavored by their unique perspective in the story, which eventually showed itself in the end of the story, casting the entire story in an entirely new light at the conclusion (a nice technique for springing a surprise ending in the conclusion).
Basically, Switch, we've coming to the same conclusion from two different directions. You're saying that "1st person is 1st person" and "3rd person is always 3rd", while I'm saying there are gradations in both 1st and 3rd, but that you stick to one and don't Switch horses mid-race.