I didn't think that you were (and having glanced at the paper now, there seems to be a lot more meat to it), but I think others will see only the plot. In my opinion, such a plot is misleading given the large variance I would expect in the rating.

It's true that the average clearly moved, but the author was trying to make a generalized inference from the average, that there was a structural break in the "true average" insofar as the measured average is just a sample/noisy measurement of the "true average". Therefore, error bars/confidence bars would indicate how likely the structural break in measured outcomes is to reflect a structural break in the underlying "true average."

The volatility/variance comes from the fact that 1. not everyone rates their experience, 2. there's variability in the experience, 3. different people have different expectations or likelihood to rate high/low, etc.

I hope that clarified what I believe was the parent's meaning.

With error bars/lines on that plot, this discussion wouldn't have been needed. There are nice ways of doing error contours - showing the 1% quantile lines on top and on the bottom.