Brook begins with several small velvet-esque spots that tend to appear most around the front of the dorsal fin and that region of the fish before the velvety appearance.
I do agree, I don't see any brook or velvet definitively in the photos, although they are not the clearest.
It could be a sting on the fish, or an infection (or both, actually). If the fish is stuck to a powerhead, it's unfortunately not going to make it most likely anyway. This happens when they're too weak to avoid.
I think what
@HotRocks meant was that on a powerhead they may struggle to get oxygen and die quickly there (oxygen may not travel through the gills well based on the pressure, depending on the direction the fish "lands" on the powerhead.)