Yes, what Puggo is saying makes complete sense. It's much easier working with digital tools because we know the framerate will always be at a constant. When you're working with film projectors (especially ones built for home use), they tend to fluctuate between speeds. It's almost never at 24fps solid. Of course it's so minute we never notice (although sometimes the sound can give it away. Pianos for example sound warbled on 16mm optical).

Because Puggo captured the sound from a projector, he has to deal with all of those subtle dips and ups in speed, whereas his picture is pretty much locked solid at 23.9fps thanks to the capturing device.

Of course, he could have just pointed a camcorder at the wall and filmed the projection and the sound would have remained in sync... But the quality would have suffered immensely.