Our daughter said it was a bug too but we have had the game cameras there for about a year and there is no shortage of bugs. At that time of night it would be a mosquito.
Do those cameras make any noise when they take a picture? I was thinking if there was a bug resting on the camera, and it makes some noise when triggered by the deer, it might scare the bug into jumping off the camera and into the picture?
Also, does it only take a single picture or a series of pictures?