I see that a lot these days with "most recent update" that I'm pretty sure is a lie. Or maybe they changed some tiny thing to make it not a technical lie.
Fiction is lies only when you want to pass them off as the truth:
"That's right -- and when you get to the human world, the Nothing will cling to
you. You'll be like a contagious disease that makes humans blind, so they can no longer
distinguish between reality and illusion. Do you know what you and your kind are called
there?"
There's in the same dialog this warning about advertising and politics:
“When it comes to controlling human beings there is no better instrument than lies. Because, you see, humans live by beliefs. And beliefs can be manipulated. The power to manipulate beliefs is the only thing that counts
... Who knows what use they’ll make of you? Maybe you’ll help them to persuade people to buy things they don’t need, or hate things they know nothing about, or hold beliefs that make them easy to handle, or doubt the truths that might save them.”
It is! Ende was raised under the esoteric Anthroposophy philosophy, and I suspect much of his works are dedicated to debunk its nonsensical beliefs. The second half of The Neverending Story is a philosophical treaty on itself (it hurts the book as an action story, but gives you a lot to ponder about).
His child books certainly have a deep second reading as adults.
After all, it claims the unreal as real. Fiction, lies.
The difference with things like fiction in books and movies, for entertainment, is that the listener of the lie, knows it is a lie, and listens for entertainment.
I would argue that a lie involves deliberate deception, not just untruth. Fiction, then, is not a lie, as by definition it is something imagined or invented, and therefore not created to deceive.