2D inkjet printers... and advanced fine art reproduction
... only basic and office models use four inks. Entry level prosumer photo printers usually use at least eight, and pro models 10-12 inks.
What they did was also already made, albeit with more sophisticated imaging systems:
https://www.designboom.com/art/oce-3d-printer-creates-identical-reproductions-of-fine-art-paintings-09-30-2013/
https://www.3dprinter.net/canon-and-fujifilm-3d-print-van-gogh-and-rembrandt
https://hexus.net/tech/news/peripherals/86429-canon-demonstrates-printing-realistic-artistic-textures/
It looks the novelty of their approach was using AI instead of more sophisticated 3D imaging, but I think from a simple 2D photo it could miss details. Correcting colors for light conditions is something photographers learn early, from simple white balance to more complex profiles - even if today sometimes it is complicated by non-continuous spectrum lights.