Under Ground Desert Temple and Ruined Portal

i was playing survival then i found obsdian in a desert and i thought my friends placed it there then i checked and i saw its a ruined portal undergground, and while i was diging it up i heard explosins and i thought they got to weird and i went in spec and checked wat it was and it was a desert pyrimand and it got exploded and i didn't know who it was but there was a creeper and skeleton down there. and I WAS SURE its not meant to be in the game.