Other mistake: When John first enters the attic room, it's a roughly 8ft by 8ft small space. Yet after he opens the music box, the camera pulls back and the area is suddenly much wider.
Other mistake: When Senator Carmichael enters the large building you can see a crowd of onlookers reflected in the glass windows watching the filming. (00:58:20)
Other mistake: When John is talking about the murder of the child Claire yells at him to stop but refers to him as George. George C Scott is the actor's real name. (00:57:35)
Answer: It was implied to be his "spirit" or "soul" that John saw.
TedStixon