Generation of a "style", even for humans, requires a feedback loop where what was created is incorporated, mimicked, and expanded upon.

An AI whose training model only rewarded images that mimicked 19th-century art would never develop a "style" outside of that. But if you had a model that was trained on 19th-century art, and then provided a critic network that rewarded 20th-century art (as well as 19th), and re-trained the network, I suspect that it would develop a 20th-century "style", as variations that previously would have been rejected under a strict 19th-century criteria will now be accepted.