In fact, initially, Suravi did not recognize the phantom behind Onika as the soul of a true Giant Dragon.
It's important to realize that in this game world, there are numerous magics that can imitate the form of a Giant Dragon, even Suravi can imitate it to some extent with his witchcraft.
But these simulations yield negligible practical effects. Only some distinct magics can mimic the true power of a Giant Dragon.
However, the anger exhibited by Song Jian's battle pet, this young black dragon, prompted Suravi to realize that the huge dragonish phantom shadow behind Onika was not some magic simulation, but rather a Dragon Soul.
Such a being can only be formed by personally slaying a Giant Dragon, then extracting its soul and refining it with special magic.
But this method is exceedingly cruel; those utilizing dragon bodies as material for crafting equipment and weapons are seen as enemies by the Dragon Clan.
If discovered, it ensures a fight to the death.