i don't think it's a complete pcb design suite, i think it use pcbdoc created and edited with AD then export them to solidworks friendly form , like step better than AD do, cause for now altium can't export the copper layout or the mechanical layout, just the 3d package linked to the component on the board and the board itself.
so i guess your first thought is the right one , just an additional tool, not a cad by itself