[Bamasgod]

Yep, slow shutter speed and movement - but you did pause long enough momentarily to get them recognizable, which is key. I think you must have taken the pic, thought the camera was done, and then moved the camera. This can be done with a flash as well (although usually performers on stage are too far away for flash to be effective) - you set the camera with an intentionally slow shutter speed but also pop the flash off. You get a "frozen"image of your subject but also the blurry motion of movement, the "trails" look. You can spin the camera, zoom in and out and get weird effects that way too.
Very, very cool shot you got there! Some accidents can end up with some spectacular results for sure.