The preds tensor represents the predicted class index for each pixel.
I.e. you could interpret the tensor as:
tensor([[[class1, class1, class1, …, class1, class1, class1],
          ...
         [class1, class1, class1, …, class1, class1, class0],
          ...,

For the original problem with 3 classes, you should see the values [0, 1, 2] in the pred tensor.