It's so funny when someone finds something Alpha players have seen from day one, and they think it's some big secret, no there is nothing special in that cave, Fallen used to shoot at you from the balcony, it was a hiding spot so we could face the lvl ?? hive and fallen that where there during Alpha and Beta, but it was pointless, at one time there might have been a patrol chest there but I'm not sure. And there are a lot of things Bungie made for no reason, some even had use during Beta, and yet didn't make it to Beta part 2.