But it also can't be a real cat. Because if it was a real cat then the cat itself collapses the the wave function. Literally any particle interaction does. Really what is important here is that us being on the outside and in a different reference frame (we're assuming we can't do any measurements of things inside the box. Think information barrier) we can't obtain any definite prediction of the cat's state, only probabilistic. The information barrier is the important part here.