Explode is an ability that if an unit is killed, it will deal X ability damage to opposing and adjacent enemies. It obeys part of general laws of ability damage, being blockable by immune, and unblockable by physical defense. However since the unit performing explode is already at zero health, reflect will have no effect on it.
It cannot be rewritten as "Sacrifice: Zap X: Opposing and Adjacent", as the effect can happen even by death from burning or poison damage.
A glitch that causes double explosion on a 1 health unit being attacked by Disease enemy would happen rarely.