The fireworks aren't actually bombs, we're seeing the perspective of the grandpa, for a moment, as what is likely a survivor of the Tokyo firebombing.
Yeah this one is less traditional horror and more pointing out the horrors of war (and war crimes on the populace, which America's firebombing and complete flattening of Tokyo absolutely was on its own, even without the later horror of the atomic bomb) and how its aftereffects are felt long long long after.