Opening one end of the box (the end marked "open") released a coil spring that caused the acid to drip from its vial onto the blasting caps; the acid ate through the caps, igniting them and detonating the dynamite.
When you opened one end of the box, a mechanism was set in motion, releasing acid from a vial onto blasting caps, which were then ignited by the acid, resulting in the explosion of the dynamite.