Not really. A sudoku puzzle is a set of squares arranged inside another, bigger square. If it were a square of squares, it would mean that you square the initial square's volume including the unit. But in this case, you're only multiplying with a count (or rather, a squared count, since we're talking about two dimensions).
? We're not talking about any units, we're talking about numbers. There are 3^4 squares in a Sudoku puzzle. You don't need a hypercube or any unit of measurement to see that's true.
