Obviously, deer are curious also. I speculate that the deer was hunting around the base of the tree for acorns, got within range of the motion detector of the camera and then heard the camera turn on the infrared light. But who really knows — only the deer.
Look to the center and then right and you will see a blurred image of the fox. For it to get that far after the camera sensed it and snapped the photo, it must have been really going fast. At least it didn’t have a chicken.