I assume it was $2000 + refund of fare difference? I would jump on this offer for a daytime flight.

I am also surprised that D1 was overbooked, but I noticed a trend this summer with full / sold out D1 cabins. I was on a number of really cheap D1 corporate tickets recently where D1 was sold out days before flight and I assume corporate discounts contribute to full D1. I can not disclose my D1 fares but sometime it was even cheaper or comparable to published PE.