I know, that's why I said 'in effect'. I was tempted to write "in the very particular case of this particular setting on this particular device", but decided against it
When I tested the dithering option on 20-30 different covers, rather than soften compression artifacts, they all looked sharpened. You can see the added noise on a computer screen, but the main effect on the device is definitely sharpening. Can't really explain it though...