Unfortunately, the screenshots are a bit small, I cannot read the numbers.
To me this is not surprising: if you average multiple values, the mean will always have less extreme values.
Well how did you create the mean displacement map in the first place?
The max error is just a statistical measure, not related to displacement in particular. It’s the width of the bars of the histogram.
If you want the low coherence areas removed from the statistics you can create a mask (coherence_mean > x) and use it as a ROI at the right side of the window.
Also, you should remove the value of the blue area, it obviously distorts the results, especially the mean.