I don't think its really all that magical when looked at as a giant component. In the context of the react-redux lib, its really similar to just having one large top level component that contains your entire state and all methods you would want to commit (but instead its called a store and actions). Everything is still unidirectional in that it has to go through that main redux provider and then gets passed back down to all the children, without the need to pass around every single possible method to each child.

So even if you have two "smart" components they are still just children of that main redux provider and therefore it makes sense that they can impact each other. The same way children can call methods that change a parents state on normal react components.