Thanks @albanD,
Managed to dial in with this code
  C = x_train[0].shape[0]
  H = x_train[0].shape[1]
  W = x_train[0].shape[2]
  flat = C * H * W
  for train in range(num_train):
    dists[train]=((x_train[train].view(-1,flat) - x_test.view(-1,flat))**2).sum(axis=1).sqrt()

Question:
So when I reshape it with view (-1,flat ) I need to use axis=1 because I want to collapse via the row.
If I were to use (flat, -1 ) I need to use axis=0 as I want to collapse via column, right?
Also, I equate both methods , double loop with single loop.it matches now.
                        
              
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Thanks once again.