It is physically possible to do it with both a bow and (some kind of) crossbow, the only question is if it physically makes sense, because indeed the energy would be distributed, so it wouldn’t work against somewhat armoured troops. I doubt a crossbow able to do that was invented at the time, and for a bow, it’s a shooting technique, although holding 5 arrows in one hand could also work (but it’s just a variation of what they were already doing of holding at least a couple of arrows on that hand). I guess the case for barbed arrowheads, put forward by A. Siddiqi, comes from the whole quote: "When I give you the order to shoot, let fly at them swiftly with a five-arrow volley (bi-al-banjakan). The people of Yemen had never seen war arrows before this occasion", which seems to me puts the focus on the arrow themselves, although if taken too literally.