Eva said it was a surprise from Ikora and the Warlocks. The EAZ was most likely created by the Shard of the Traveler, which has affected the surrounding terrain by distorting gravity and wildlife. These effects can be seen close to the Shard, though not nearly as severe as in the EAZ. The enemies are all probably there of their own accord. Fallen remnants have been encamped around the Shard longer than anyone, the remnants of the Red Legion have been around the Shard in attempts to hold their fortifications, the Taken no doubt came for the Light, and the Hive probably came to attempt some nefarious deeds with the Shard. My best guess is that the Warlocks only organized the chest reward system and other minor things.