why this model is not care about the label of taget dataset?..

[Miao]

_, domain_output = my_net(input_data=t_img, alpha=alpha)
err_t_domain = loss_domain(domain_output, domain_label)
err = err_t_domain + err_s_domain + err_s_label

I found here you backward the loss of three part...
but I think the taget dataset's class is the most important..
why this model's loss is not care about the taget dataset's class label?..