This is why, in my responses to this and the similar example about being flown by the eagles over the woods, I emphasised that context is all-important.
Suppose the game being played is Burning Wheel, and one of the players declares, and succeeds in, a Spiders-wise check to establish that there are great spiders in the Gnarly Forest. And then the PCs head there. The GM who presents them with Orc encounters is coming close to force - not honouring the intended result of the successful check. Whether or not it is illusionism will depend on how well the GM conceals the force. This is hard in BW; there are other systems with weaker action resolution frameworks which therefore make it easier.
Consider a D&D game where the GM has a rumours table, and there are two true rumours on it: that great spiders lurk in the Gnarly Forest; and that the Grim Chasm is dotted with Orc patrols. And suppose the PCs (and thus their players) acquire both rumours. And the players therefore decide that their PCs will go to the Forest, hoping to fight spiders. Finally, suppose that the GM is intending to spring an Orc encounter on the players no matter what! In this case, the whole thing with rumours and apparently giving the players the choice of which place to go to, is all pointless - it has the appearance of mattering, but it actually doesn't.
I think that would be an example of illusionism. And frankly I reckon stuff like that is probably pretty common in the RPGing world. Rather then the rumours serving the function that they once did in Gygaxian play (for the classic Gygaxian rumour table, like in KotB, acting on the rumours actually does make a difference to what is encountered), they are simply there to give an impression of a "living, breathing world". When the PCs hear rumours of spiders but nevertheless meet Orcs, this even allows the GM to drive home how "living and breathing" the world is!