I don’t know for sure, but I think this value probably is platform specific. For example in CSS it’s 0.5 of Figma’s value, but somewhere like iOS or Android (maybe, I don’t know for certain) the value might match Figma better.
I think the main question here would be does it look similar in Figma & CSS if you use the 0.5x values from the inspect panel? Or do you find that the original Figma’s exact value more closely resembles CSS? If the latter, indeed that might be a bug.