It is a combination of both, if you have a clean anti-aliased image, that means that the pixels at the edge of your objects are inbetween values of grey (on the depth pass) and frischluft can’t figure it out if that exact colored pixel should be blurred or not, thus the dots…
theres is no solution to that, though you can adjust the settings and make it less visible, or you can render the depth aliased at a higher resolution and let AE do the math while scalling it down. I’ve had better and worst results doing this.