As a photographer I have to add that one of the main reasons he may have indeed captured spirits is actually down to something he probably still hasn't noticed. ISO folks, if you want to capture spirits then the higher your ISO the better your chances will be. You need a high ISO to shoot in dark situations but consumer grade cameras don't always handle ISO values very well, as you raise the ISO you gradually add noise so if it's very high then the image will be very grainy. I mainly shoot rock concerts so I'm constantly working in the dark with an ISO of about 1600 or higher, I can go very high with my ISO before I notice noise because it's industry standard equipment but the downside is the faster the shot then the more frozen my subject and you need to have a sense of movement when documenting live music. He states in the post that he shot in RAW so he may have been using a professional or sem-pro camera, his ISO was naturally high for the scene he was shooting so without knowing it he actually gave himself some very solid settings to capture something the naked eye so often misses.
Just recently I was doing a spirit session and talking to many of my regulars, I had 3 cameras in the room because I'd recently covered a show. When I picked up the In-fared camera and asked would anyone like their picture taken a lady clearly told me she didn't want to be filmed, while a male said "I'll film you". My own two cents on the high ISO theory is pretty simple, ISO lets you shoot incredibly fast and spirits tend to show up more clearly when a faster shutter speed is used. You would assume that a long exposure would mean a higher chance in catching the spirits but they move so fast that you would actually miss them. I believe the guy, I think he had the right location and the right settings. One of the main explanations sceptics would jump to (apart from the obvious photoshop) would be a long exposure capturing people walking through the frame but I know by looking at those street lights that he didn't have the shutter open long enough to get that effect. I'd love to see the RAW myself, if real then it's one of the best digital spirit shots I've seen in a long time.