>"Paradox pokemon are imagined into existance! They aren't real!"
>"That's just for China, they can't have references to china!"
In truth, the answer is not obvious, and probably won't be until the DLC, but till then, there is a post game scene that strongly implies extreme fuckery and that there are issues with the claim they are time displaced pokemon.
During a certain talk with Arven in the post game, he will explicitly point out that most people thought the Violet/Scarlet book was hogwash, and he only turned to the HM Herbs out of desperation, and was shocked when they worked. He shows you the page with the disk pokemon on it, and points out that the page is smudged and illegible in every single print of the book, something he finds off. He will then mention how the book was what inspired his parent to make the time machine, but then he will immediately point out that it doesn't make sense then how paradox pokemon existed before the time machine, like the book points out.