Color contrast too low, but element good visible

I am checking a software against the software ergonomic requirements of WCAG 2.1 Level AA. On part is the colour contrast, which must be for graphics 3.0:1. In the following graphic the orange part is for users without any disabilities very good visible, however the tool "Color Contrast Analyser" show only a contrast to the white background of 2.0:1.

So the graphic does not meet WCAG 2.1 Level AA. But what is the reason? Again: the orange part of the graphic is very good visible. Might it be an inaccuracy of algorithm for calculating colour contrast? Or is it just my personal sensation?

Any other ideas?