Probably called eelpout because they look a lot like them. As far as i know the "real" eelpout is an ocean species. Im not sure thought but when i translate eelpout to Swedish i get "tånglake" which is an ocean living fish that looks almost like burbot but you can see clear differences between them. Not a big deal really in the ol' days they called them freshwater cod over here.
EDIT:
Apperently Ling, Cusk and eelpout (all three are names I've heard people using when referring to burbot) are three different types of cod-like fish all living in the ocean. It was confusing for someone like me coming from Sweden because I had a hard time figuring out which one it really was. Why don't people just call them burbor? lol