Highlight radius inserts blur at 0px

Hello, everyone.

I'm  a beginner at Photoshop and utilizing de CS6 version.

In the advanced options of Shadows/Highlights Adjustments, we have the 'radius' option for both Shadow and Highlights and, according to Adobe help website, it 'controls the size of the local neighborhood around each pixel'.

So, as i low the highlight radius, with amount and width set to 50%, the image gets "sharper". But that's until 1px. When i set the radius to 0px, it doesn't follow the pattern and the image gets a blur effect, as you can see in the image.

The question is: What happens when the radius of Shadow/Highlights adjustments is set to 0px?