I would probably consider books to be a form of art.

Art is very varied, its not just paintings or photographs. Video games can be art, music can be art (artists!), an eloquent dance can be art.

I agree books are a form of art.

However I wouldn't call AI training on text in books "stealing art"

Do you consider reading a book and remembering what you read to be a form of stealing? How about writing a book review?