What is pseudopolymorphic behaviour? Either they are polymorphs or they are not.
If you are talking about solvates, then yes, different solvates of the same host compound are often isostructural and can have very similar lattice constants.
One structure is simply the compound itself. Other contains one lattice water. Whether it belongs to solvomorph or polymorph? Or can we classify the compound to any other category? Both have same lattice constants. But packing and Supramolecular features are different for both.