Yes, it is a multiple barrage. Each (undamaged) vehicle fires four small blasts, if in a squadron you could have up to 12 blasts. First is the only one that scatters 2d6 (possibly -BS depending on range and LOS). Bear in mind that it is twin-linked, so this can be re-rolled. After that, each additional marker just gets a scatter die (which can also be re-rolled, per the WD article on the Wyvern) to determine it's placement.