In any case, the opponent was an ancient dragon who lived for tens of thousand years.
In recent years, there weren’t too many eye-witnesses being treated to the view of an half-imaginary monster. It seems that even the scholars researching ancient dragons couldn’t unconditionally confirm their existence.
Seldomly being seen, ancient dragons were high ranking members within the dragon race3 according to Burkhart-san, who had already defeated a drake before. Therefore they were a species close to half-spirits.