If the AI company bought their book, then they didn't give it all away. If the AI company obtained it indirectly like a library or 2nd hand, then the author has already been paid when he first sold it. In either case, he could have refused to be so liberal in sharing it if he didn't want it to be used like that, but he preferred to make some money instead.

Does a torrent count?

If buying one copy of a book entitles the ai company to train on that data and redistribute information derived from it in perpetuity, then why shouldn’t a rival ai company be allowed to train on tokens from say OpenAI and redistribute information derived from the OpenAI model also in perpetuity? The rival ai company paid for the tokens, after all.