When the game first came out enemies use to spawn from that cave every 6 seconds. Quite often to several guardians firing continously, then after a minute you'd go pick up all the engrams they dropped and do it all over again. People spent hours 'farming' legendary items this way instead of competing in any activities. Once Bungie increased the spawn timers on all caves, this became a thing of the past, this pile of remains being the only reminder of that bloody past.

It was just an Easter Egg from the old "Loot Cave" I believe.