He definitely spammed explorers more than I would have. It did work well for him since he was able to get a lot of resource pod bonuses and excavation bonuses. He also uncovered an impressive amount of the map which will allow him to easily place his future cities in the best spots. But I think it only worked because his neighbors were far enough away as to not present any military danger. He has got a very solid industrial foundation now with which to crank out a military pretty quickly (and he took some quests that will further boost military production). He will be able to catch up military pretty easily. But the strategy does seem risky because if the AI had been closer, he could have faced an invasion before he was ready to defend himself. In civ5, it happened to me a couple times (before I learned my lesson) that I would focus too much on infrastructure and neglect my military and get crushed as a result. So now, I am a little paranoid about it. So, I tend to build several military units early just to make sure I am not defenseless if the AI DoW's me early.