The statement "Each confidence interval in the middle plot is an approximation of the width of the sampling distribution in the bottom plot."
I would suggest not to link confidence interval with the width of sampling distribution in the bottom plot. The green shape in the bottom plot was the theoretical normal distribution. Because the population sd is fixed, the shape of sampling distribution is also fixed (se = population sd/square root of input sample size), which does not depend on the randomness of confidence interval from random samples. It would be more clear if we emphasise about the only connection between the middle and bottom plot is to collect all the sample means from the simulation to make a histogram in the bottom plot.
https://github.com/statistical-reasoning-course-dev/Statistical-Inference-Rewrite/blob/bb60b4129963962013c83c2cb9e2f9713b975d34/03-estimation.Rmd#L407C210-L407C335
The statement "Each confidence interval in the middle plot is an approximation of the width of the sampling distribution in the bottom plot."
I would suggest not to link confidence interval with the width of sampling distribution in the bottom plot. The green shape in the bottom plot was the theoretical normal distribution. Because the population sd is fixed, the shape of sampling distribution is also fixed (se = population sd/square root of input sample size), which does not depend on the randomness of confidence interval from random samples. It would be more clear if we emphasise about the only connection between the middle and bottom plot is to collect all the sample means from the simulation to make a histogram in the bottom plot.