Always has been. Just yesterday I was explaining AI image generation to a coworker. I said the program looks at a ton of images and uses that info to blend them together. Like it knows what a soviet propaganda poster looks like, and it knows what artwork of Santa looks like so it can make a Santa themed propaganda poster.
Same with text I assume. It knows the Mario wiki and fanfics, and it knows a bunch of books about zombies so it blends it to make a gritty story about Mario fending off zombies. But yeah it’s all other works just melded together.
My question is would a human author be any different? We absorb ideas and stories we read and hear and blend them into new or reimagined ideas. AI just knows it’s original sources