You are right. Any weapon used in an assault is an assault weapon. But it isn't about the assault: it is about trying to make something sound scary and thereby illegal. And not really being about to exactly describe what it is except that it is scary.
That would have read: "And not really being able to exactly describe what is is, except that it is scary." Must be why they let you preview before you post, huh? Excsue me folks. I'm new here.