Firion vs Dummy Warrior of Light (Oddity)

**Replay Edit. I left the heath bars on to show the damage done...... I was going through Firion's story to get 100% (i was at Lv.100) when i stumbled across this strange scenario which has happened to me a few times before,but i've never saved it until now.... Firion's StraightArrow is a long range (very long range) attack that can be held onto for a short time (for "aiming accuracy"). It's a one-hit direct HP attack upon contact. In this short video, it shows Firion's StraightArrow back firing--blowing up in his face dealing his own BRV to himself as the dummy Warrior of Light blocks for a split second. Can anyone provide an explanation as to why this happens other than it being a glitch?