What the players know isn't the point. Most of the time they won't know. That doesn't make it okay to deceive them.
So let me dig in to a few points going like 5 pages back.
you have stressed that if the quantum ogre always appears than that’s railroading, and people are fighting you on that definition. I will actually agree with you here, it is a railroad….but I don’t think railroading is necessarily a problem, it’s a matter of degrees.
So let us take the stance that such a railroad does in fact remove a player choice for this argument….but what if during the encounter the players still have full agency on how to deal with the ogre (run, hide, talk to it, fight, etc). So the player was still offered choices….how many choices are required before the game becomes “unacceptable”?
let’s take that a little further. Let’s say the players chose to fight (a meaningful choice). The fight lasts for 4 rounds, a player making 4 choices that impact the fight. So the player made 5 meaningful choices here. If I had allowed the party to ignore the ogre, there original choice is validated but they lose the ability to make those 5 choices…meaning I have denied my player a total of 4 extra meaningful choices. Am I now a terrible DM?
The REAL answer here, is railroading can only be determined through the amalgamation of encounters. If the DM denies choice in one scenario but allows it in another, overall things are fine. It’s always about a matter of degree, you can never look at one scenario and go “this is a railroady DM”.
And lastly on the quoted note about deception, this example. Let’s say during a combat a player decides to improvise, and wants to slip a firebomb into a creature’s pocket. The DM asks for the check and also notes that “that pocket also had a container of oil…so the bomb will have a big effect!” But…that’s a lie, I just made that up for this moment, that was not planned ahead of time. Has my deception ruined the game…or just delighted a player and encouraged them to improvise in the future?
Again it’s always a matter of degrees. If I make something good up for the players every time they improvise…then the magic of disbelief is lost…and the improvisation no longer seems special (or players may feel they have to improvise to get bonuses). But used on occasion it can delight players, and shake up the game in interesting ways.