I took a closer look into the history of A350 MSN 720 (N527DN), and I agree with others that it must have been a mishap by NG to use the old winglets.
According to a photo on Planespotters, the frame was seen unpainted on November 29, 2024:
https://www.planespotters.net/photo/1685409/f-wznk-delta-air-lines-airbus-a350-941. No one knew about what the special livery would look like around that time, and NG might be no exception. However, around the same time, NG produced several A350s with the new winglets, such as the Delta Olympic liveries, Air France, and Emirates. So there must have been some mixups with their production.