? You have a right to be skeptical...
Now, here is the original page:
https://en.wikipedia.org/wiki/Swamp_eel
This is where the length comes from.
Now, to begin, these fish are also listed as 8.5cm on FishBase, so this seems consistent. Next, many earthworm species are smaller than American species. There are several species of earthworms, many of which small enough to be eaten by such a fish. Now, as for the fangs, yeah, swamp eels do not have fangs. That's just straight-up misinformation. As for the survival tactic, floating on the surface is not uncommon for air-breathing fish like swamp eels. I have observed young specimens of larger species exhibiting similar behavior numerous times. It's possible that there are a lot of floating plants in its range, which it could easily blend in with.
Now, to support your argument, I totally think it's possible that someone made a typo, and another person, followed by FishBase, ran with it. However, I am remaining somewhat skeptical due to the fact that that is pretty much impossible to prove, and FishBase is generally reliable. Moving on, even though some are small, many earthworms are in fact very large in comparison to these fish. I'm not sure exactly what earthworms are native to that range. Moving on once more, swamp eels, once more, do not possess fangs. You are still right on that one. I also agree that, unless there is a large amount of vegetation and other forms of cover on the surface, then the survival tactic they allegedly use is admittedly sort of wonky.
So, all in all, not sure. Seems to be some conflicting info here.