Nothing dumb in wondering about an unfamiliar setup.
The idea is to get detailed fire and a properly-exposed dancer in one frame. Tricky for a number of reasons, but mostly because the fire looks best when generating long trails, and the dancer looks best when frozen and sharp.
The camera is set up to produce long fire trails (0.8sec exposure) without over-exposing the fire and losing detail (thus, f11 at ISO100). But without the flash, the dancer would not be visible (just a black blob with whatever light she caught from the fire) at these settings. So I set the flash for second-curtain sync (which makes it fire at the end of the exposure instead of the beginning), increased the power to expose the dancer at the desired level, and zoomed the flash head (which tightens and intensifies the cone of the flash's light) to create the vignetting.