That photo was taken 6.39am KL time or 5.39 Vietnam time. Sunrise in Ho chi Minh is ~6:04 am local time.
So i doubt it would be pitch dark at 5.39am.
Also the sunrise from 11,000 m would be around 7 minutes earlier. Now i understand that won't illuminate the ground but it certainly won't be pitch dark when the guy took the photo.