Your code snippet seems to work and returns the right result:
x = torch.zeros(5,3)
t = torch.tensor([[1,2,3], [4,5,6], [7,8,9], [10,11,12], [13,14,15]], dtype=torch.float)
index = torch.tensor([0, 2, 1])
x.index_copy_(1, index, t)
> tensor([[ 1.,  3.,  2.],
        [ 4.,  6.,  5.],
        [ 7.,  9.,  8.],
        [10., 12., 11.],
        [13., 15., 14.]])