A question about scheduled sampling

Thank you for such a fascinating job.
In https://github.com/da03/markup2im/blob/main/src/train.py#L197, we sample $y_{t+m}$ from $P(y_{t+m'}|y_{t+m'+1})$. The code only considers the mean $\mu_\theta$ without $\sigma_t$. I don't know why. Can you tell me, please?