Exposure rate...
I'd say it was likely that this might have been done with a film camera. With the correct film speed, an open shutter and just the right aperture settings, the film will only pick up the sparkler because it's so bright. The person holding it is moving to fast to register.
Now, because the couple is standing still, they will start to register, right at the end of the sparkler run, shoot a massively bright fill flash at them to finish the exposure and close the shutter.
I'd say it was likely that this might have been done with a film camera. With the correct film speed, an open shutter and just the right aperture settings, the film will only pick up the sparkler because it's so bright. The person holding it is moving to fast to register.
Now, because the couple is standing still, they will start to register, right at the end of the sparkler run, shoot a massively bright fill flash at them to finish the exposure and close the shutter.
-OR-
Photoshop and layers.