Yes, I have always understood the quoits to refer to the stones in the circle inside the henge. One devil threw many quoits, therefore, the devil's quoits.
Prior to this thread, I always assumed a quoit, in the megalithic sense, to be a stone or set of stones. And I'm not about to start arguing with the OED. It's never lied to me before. ;)
My swing-vote has just swung back to my original assumptions. The "quoits" are the stones. Of course they are! :)