It’s a technical term. 
What it means for the histogram is that I have to horizontally scale the histogram graphic to the window dimensions minus a pixel or two, I forget now what it is. That way, those vertical ascents at the ends don’t end up in the window borders.
Can’t tell from the JPEG, but you have a lot of blue in the sky that falls in the range 253-255. From the raw, RT is in a better position to evaluate the clipping done for the output, so I’d put stock in that .02%.
This is exactly why I ‘scooched’ my histogram scaling.