It was likely shedding. The burst of energy was to promote the shed, what you saw was likely flakes of skin. Lionfish will shed their outer layer(cuticle) from time to time. Possibly from a change in chemistry and as protection from anything trying to attach. Usually not much to worry.
Its not good to feed minnows, they are high in thiaminese which will bind vit B1. Vit B1 defiency is likely one of the leading causes in lionfish deaths, as well as other species. If you are feeding live; ghost shrimp, guppies, and mollies are better choices. If it's a volitan, getting them to eat a varied dead diet is usually pretty easy. Feed krill very sparingly, as it is also high in thiaminese.