It is supposed to be one or the other if you use the material editor, because you need to tick "desplacement", and then click Import normal map. But if you check the function editor, ypou'll notice that the nprmal map has been assigned to a Normal output, so you can connect a displacement map/function to the Displacement output.

But when doing so, you can't decide of a strengh value for the displacement, and if you check your render, it seems the displament hasn't been applied, so I'm not 100% sure, but it does seem you can't use displacement and normal at the same time, nor bump and normal at the same time....