question: why is the viewer entity coupled with other entity

[jaimesangcap]

According to this feature-sliced page

Slices of the same layer cannot use each other directly, and their interaction and composition should be determined on the upper layer, relative to their current one

But the entities/viewer/model/hooks, refers to both wallet and book entity.

Isn't violating the principle? What is the reasoning behind the coupling?
Just curious if there is another way to tackle that particular design, like moving it to the upper layer?