My guess: it had a little freak-out & bashed into a rough/sharp bit of decoration - I have a filament barb like that, have since rethought use of dead coral in decorations. 18mo later & the fish is fine - still not much mouth, so takes a little longer to eat anything, but otherwise good.
Hmmm... Don't look like it. The tank hasn't got any decorations except for lots of soft plants and floating guppy grass.
Tried to keep it clear as possible so that the fishes have got sufficient space to move around