I think a bit more is going on, a possible (typo) bug.
Also. No. there is 0 damage being done to the reactor, destroying it. (according to the events log)
As I've been paying more attention to the massacre, I've noticed reactors are always destroyed by 0 damage, not always 0 casualties when destroyed though.
Actually my lone surviving ship was bombarded by a secondary salvo, the first hit did 3 damage to shields, 1 to shield generator, 0 to reactor, destroying the structural integrity.