Sundance. I don't know what you could have done wrong. Maybe you purchased "collard-flavored oak wood" by mistake?
Seriously, I can't imagine that you did anything wrong. Cooking any greens for 4 hours would have to make them tender, so I have to wonder about the bag you bought. I cook collards, fresh or frozen, much the way you described, and 1 to 2 hours is all it ever takes.
Beyond that, your overall meal sounds heavenly.