Copyright covers creative expression, not functionality. The code and unique design elements would be protected, but not the idea of a grid or guessing letters, etc (which all predate them anyway). Even the word list is difficult to claim protection to if it was generated by algorithmic filters on dictionary words (it probably was) because then the selection also isn't expressive.

So I can't copy their code or exact look, but I can definitely make my own version legally.

What's the point? Yeah I don't know why they spent money on such a simple concept either. The copyright protection is far more useful when the thing has enough expression that clones won't be indistinguishable anymore.