I feel the partys actions led to their demise, they knew the number and power of thier foes and did not take enough precautions after thier raid on the ogres lair. The DM played the monsters to thier potential and got a TPK, I would not consider him to be a killer DM. Hopefully from this the players learned from the mistakes they made, but also hopefully the DM also learned that while he was justified to use the ogres to the max of thier abilities there were several viable alternatives to the TPK that would not have seemed like he was going easy on them. Also when the players chose their course of action a few hints from him about how close to the ogres lair might have made the players realize how much danger their characters would have been in.