Well, I guess part of it is that it was effectively a generation ship, so there’d have been plenty of “civilians” (if such existed) and children and such among the casualties.I thought it was the most enjoyable episode of the season, but I have mixed reactions to the plot twist of they were all humans. It seems like the point was to make Kirk realize he would have hard decisions, but everything he did was justifiable because the scavenger attacked them and ate up a planet. Making them humans seemed like a sympathetic leap but I'm not sure how earned it was. I think they needed to come up with a better reason for Kirk to feel guilty if that was the point they were making, but they could have stopped it at Kirk being able to lead his crew through a dire situation.
One does wonder why they first started marauding human colonies rather than contacting them and “coming home”, and how they got technology more advanced than anybody they met.