Statistically indistinguishable by what measure? One of many we could come up with, no doubt. If an expert were to look closely at this, perhaps they would also distinguish them, by something the statistics didn't quantify.
An expert forger would be trying to make a painting that is literally indistinguishable from an actual Rembrandt, which is much harder. The GP's point was that something that can fool an algorithm is no more deserving the label "new Rembrandt" than something that can fool a human.
By what measure? The measure of as many experts as you can find.
Copying a specific painting is a very different thing. It's hard for entirely mechanical and chemical reasons. Trying to make a new painting that blends in is much more interesting.
I don't mean copying a specific painting, but creating something that looks to human experts like a previously undiscovered Rembrandt. This would be a lot more impressive than creating something that fools a particular statistical algorithm.
What has suggested to you that the goal of this program is not creating something that looks to human experts like a previously undiscovered Rembrandt? (With emphasis on 'looks'; they're not trying to trick forensics)
They don't seem to have asked a lot of human experts for input. I think if they had done, the finished article would look different.
In fact it's nearly impossible to nail down provenance of any painting without an historical paper trail.
Auction houses regularly pay academics to make statements about provenance, but the statements are always questionable if there's no definitive record of sales and ownership.
The goal is something that looks like a real Rembrandt. Not something that has a convincing paper trail, or something that correctly carbon dates. The point is not to trick anyone, but to ask the question "based solely on your knowledge of how Rembrandt paints, can you tell if this is one of his?"
An expert forger would be trying to make a painting that is literally indistinguishable from an actual Rembrandt, which is much harder. The GP's point was that something that can fool an algorithm is no more deserving the label "new Rembrandt" than something that can fool a human.