That album did not bring them fame. It may have been integral in getting them a shot at getting signed, but I don't think there was any fame involved at the time.
In any case, "covering" a song is not stealing music. And it is in no way comparable to downloading music from Napster illegally. Almost every band starts with cover songs. And if a cover song is released, it is done with the original artists permission, who are also credited on the album. How is this stealing?
Plus, it was a friggin demo. Not an album. Different. They differ in intent and demos are not typically sold.