I think you should write to GardenWeb and suggest a revision. You sound right on to me.

earthworms is one word and composting worms apparently are still classed as earthworms. Interesting the use of the English language.

Earthworm is the term that further classifies members of phylum Annelida from their aquatic-specialist relatives. They are called earthworms because they are found primarily on land. Although composting worms would rather live in rich compost than in impoverished soil, It really isn't enough reason to change their designation. If any change is in order, it would be land worms... though that isn't necessarily accurate either.

As far as I have seen, earthworms and compost worms will both live underground when they are not trapped in a human-wrought container. Compost worms, like EF worms, will prefer fresh rich deposits of nutrients for breeding wherever those deposits are. A trick my father taught me for always having a supply of red wigglers for fishing is to bury your fish cleanings in a spot that you will remember, and then dig that spot for more worms next time you go fishing. It was effective and notified me at an early age that redworms seek nutrition regardless of where it is in relation to the soil strata.

I grow EF worms in a compost bin now, but I also use those worms underwater for turning greenhouse clippings into duckweed for my fish. I also use them for keeping my aquaponics filter bags free flowing and solids separator volume low. I dispose of dead mice and rabbit cleanings in my worm bin and I see more worms there than in any other picture or video of other people's bins, but they still function well underwater and undersoil. They are earthworms by name, but only because they have to have a name to exist in language.

When I introduced plants potted in soil to my attempt at a wicking table, they took a turn for the south from being too wet. One of the plants recovered quickly as mounds of worm dirt appeared. I added my compost worms to all of the potted plants and they all recovered promptly. The compost worms then started feeding in the bottom of the wicking table water at night and returning to the plant soil during day. The dirt had little food, but was safe and dark, so it made sense. In the fish tank, they keep their faces under the gravel to eat, but float their back-half up in the free water for gas exchange (so they can breathe). Since they are not specialized for water with predators, they are more accurately considered landworms or earthworms.

Compost worms are still earthworms as long as you don't want to cheapen their evolutionary achievements to some human garden utility.