of course it's a secret passage, it's literally just destroying the wall to make a NEW passage...or maybe the path revealed behind the wall really was secret and it's just that no one was dumb enough to randomly go smashing walls in a trap and monster filled dungeon and thus no one was able to find it before? I mean, making secret passages with no entrance or exit through an underground castle would certainly help keep them secret until you come along and brake down the walls a few thousand years later...unless someone used earth based mapping magic...although I suppose he could layer counter detection magic, standard wall reinforcement magics like are probably on every other wall in that place, and purely physical walls to create the illusion that there is no path beyond