My opponent casted Armageddon and probably also played out a strip mine on the same turn (is on top of Armageddon in his graveyard and wasn't there before) and activated that, too. However, not all of my lands nor all of opponent's lands were destroyed in the process. Unfortunately I could not determine the exact order of events as the whole thing took place real fast (Armageddon was cast for sure though, the regarding popup showed up).

See screenshot as well.