At the risk of stating the obvious, it's easy because your light is aiding the predator. The prey are relying on the dark to protect them.
I've been trying to work that out looking at the video. I was following the Conger with my light as it was moving so anything outside of what was in the light would have been harder for him to see. He also keeps bumping into the corals so I was actually worried I was blinding it with the light rather than helping it