Yes, nn.Linear expects the batch dimension to be in dim0.
However, in the tutorial you are either providing the input letter by letter (thus the seq_len is missing) or you are slicing the encoded word tensor, so that again the seq_len dimension will be missing.
Here are the example cells:
input = letterToTensor('A')
hidden =torch.zeros(1, n_hidden)
print(input.shape)
> torch.Size([1, 57])

input = lineToTensor('Albert')
hidden = torch.zeros(1, n_hidden)

output, next_hidden = rnn(input[0], hidden)
print(input[0].shape)
> torch.Size([1, 57])

As you can see, you are passing only [batch_size, input_size] to your model.