Legion-8 wasn't flustered by the sudden intrusion. He expected the dragon king or the dragon spirit to show up. This is because he has the bloodline of the dragon king at one point or the other.
For One he is still in the dragon plane so the dragon spirit can reach him. And as a being on the level of a world god or more, the dragon king's bloodline is more than enough connection to reach him. If Tssandulighafan can reach him through a mere imprint, then the entity who created the dragon race with his blood can surely do the same.
Even though he was prepared for his visit, Legion-8's heart sank when it happened. It is because his situation has become worse now that a world god has interfered.