Your ABLS is kicking in. Active Brake Limited Slip, so the spinning wheel had braking applied to it and allowed the non spinning wheel to get power transferred to it to get you going. The Open diff would normally transfer power to where it is easiest, or the wet wheel, where you were slipping. Braking evens out the speed, so then the open diff applies power to both axles more evenly. You do not really have a true Limited Slip Diff, you need to buy the Truetrac to get that.