Hi, I've seen snowflakes nip puffers, and their skin is very white underneath, so I wouldn't rule that out just yet. It could have been a one time thing.
It is sometimes difficult to see fish lesions taken under blue lights, I might be able to tell more if you can ramp up the white lights. Also, the focus is kind of off, sometimes a short video gives better focus.
I presume the fish is still feeding fine?
Jay Hemdal