Hm, the picture is hazy but by the size and shape of the pieces, it looks like it could be hagfish which is not a true eel like unagi/anago.
ETA: It is, indeed, hagfish. Looked up the menu on yelp. Might be a mistranslation, as eel in Korean is “jang uh” and hagfish is similarly named “kkom jang uh.” Have not actually tried this fish myself - curious to know how you felt about this dish.