Solved by KFrank in post #2 
              
              
                Hi Rohit! 

Batch is a single “holistic” tensor of shape [3, 3, 256, 256].  It is 
not a “collection” (in the sense of, say, a python list or dictionary) of 
three 3x256x256 tensors. 

Pytorch is doing some moderately fancy stuff with python here. 
This is not simply assigning image to the 0 element…