That's the difference with cross-wound (like Aurifil cones and others where you see the thread wrapped sort of on the diagonal/criss-cross) and stack-wound, where the thread is wrapped more like a straight line around the diameter of the spool.
Mounting a cross-wound spool/mini cone on the wrong holder (cross-wound has to come off the top not the side) results in tangles/knots. Straight-wound thread needs to come off the side of the spool.
I've always heard that but my FW's and 301 don't seem to care. I use Aurifil on the spool pin without a problem.