Flies around
Sees a dragon "hmm looks like it's distracted"
Kills the Dragon "I wonder what it was looking at, oh well guess I'll never know"
Flies off
Meanwhile not 2 feet away from the dragon is an old knight a horse and a carriage.
Hmmm... seems like our boy is lacking in spatial awareness. That seems pretty strange for a hero. Or maybe he can't register things that are below a certain power level unless he actively tries to acknowledge them? That also seems like a pretty bad trait for a hero. He would miss out on damsels in distress or oppressed people if he wasn't aware of beings weaker than himself which would just make him an OP battle junkie, not a Hero.
Also it's not clear if he was reborn into the same world or different worlds, so it might not be isekai even if it is reincarnation.