Could be. They relax their ears for a number of reasons. When they are submitting to something/someone, afraid, or sometimes REALLY sleepy. Also sign of being sick if the ears stay down continiously. We have a Doberman who keeps her ears down/back when she's really tired.
There are different reasons for dogs laying their ears back. Dogs communicate through their eyes, ears, tail, body position & even the way their hair can stand up at times. And then there are some dog breeds that just naturally look like their ears are laid back when they're relaxed. If a dog is frightened it will lay it's ears back & cowwer, dropping it's tail between it's legs.