Yes it is probably due to AI training. The clue is that it's bulk orders driving the increase.
The annoying thing about the article is the hand wringing. If anything this is the least dubious way to acquire training material. They are paying the correct party to get that material. AI training is at least as transformative as throwing the words into an inverted index for web search.
One thing this demonstrates is that there's still training material to be mined that's original, and high enough quality to have been published on paper. This source of material won't get mined out until all the similar material originally written in major foreign languages get scanned and translated for training purposes. We are in the gentle slopes of the lower foothills of the never gonna be AGI so I'll call it singularity.
The issue people have with it isn't about copyright. It's about how offensive it is that AI companies are mass buying and then destroying physical books by the millions. It's the same reason people were outraged when those two fools chopped down the ancient Sycamore tree at Hadrian's Wall. "But it's just a tree!"
No, it isn't. It's much, much more than that. There is something inherently revolting about pulping billions of pages of literature. Whether they paid people for the books is completely besides the point.
> If anything this is the least dubious way to acquire training material.
Yeah, I emotionally felt a little upset because books are being destroyed and I don't like that. But rationally, this seems very much like a win-win.
The second hand bookstores are getting revenue that they otherwise wouldn't be which means they have an easier time staying in business. AI companies get their materials legally. And it possibly pushes a second publishing run which ultimately benefits authors.
I think the only way this is possibly "bad" is if a rare/hard to get book is destroyed from these ventures. That would be horrible. But I doubt that's very likely as there's almost no such thing as a rare book that AI trainers would be particularly interested in.