when the quilt is finished/bound & laundered- those will more than likely disappear-
they happen because the needle with thread- goes up & down- catching on the batting and taking some of it along- generally it sticks a little bit to the thread- especially when using cotton thread- polyester or silk threads don't (cause the batting to stick) so much- can also be a small burr on the needle-
happens with other batts too- not just W&N---and just noticable because it's no black- but really will more than likely disappear when the finished quilt is laundered.