Very cute dog!! I love greyhounds!
I have borzoi and their ears do the same thing. Most of the time the ears stay down, but I have noticed that many tend to do that more as they get older. It almost feels like the ear leather gets stiffer with age. Starm, my 10 year old has 1 ear up most of the time he is outside. When he is in the house and bored they are both down.