I believe a glass eel refers to the postlarval stage of a newborn. It would be extremely small and transparant. If the fish you saw was very, very small than that's my guess on it.
I'm not sure how to determine what type of eel it is. You'll have to wait and see. I wouldn't buy them in the glass eel stage as they are likely very sensitive and might die on you. You also don't want to end up with baby fire eels if you don't plan on owning a 300 gallon tank someday.
Photos or a good description would help ID it if I am wrong.