No. It's just an odd reflection.

Demonic beings ARE real, but this isn't one of them. If you ever run across the real thing there will be NO doubt in your mind. They don't hang about to make silly faces in reflections, they do things to cause serious torment and despair.

People tend to attribute a lot of things to demons, but most of them aren't.

It's kind of like being run over by a truck; you don't have to ask yourself if you really got run over or was it maybe something else. A real demon is pretty unmistakable!