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They didn’t misunderstand. If you look at the images included in the paper (this link has them inline: https://journalofillusion.net/index.php/joi/article/view/983...) you can see that it is an illusion that can be created with 3D printed objects.

The linked STL is a different Kokichi Sugihara illusion - by the same creator as this new class of illusions, and part of a body of work in this field that this appears to be a continuation of.

https://en.wikipedia.org/wiki/Kokichi_Sugihara

But it is. Those are objects that are mirror symmetric, and the apparent direction they're facing depends on viewing angle, creating the illusion that they haven't actually been mirrored.