Yay! I'm not the only person wondering about it. Guess I'm not that dumb
May be as BigC says it's just the way the forum has termed them. Or is it this? I heard that in the wild they live in small pools like thingies and at the dry season when the pools are empty, even though the fish die their eggs survive. As soon as the rainy season start the eggs hatch and you can see these fish in small pools everywhere.
You are referring to annuals here, not all killifish are annuals, there are three catagories which you can loosely divide up killifish species by, they are Annuals, Semi Annuals and Non-Annuals. But it is not this that has made the Mods term Killifish as Oddballs.