As the Demon race envoy appeared in the blood gnome king's palace, it indeed caused a momentary shock to Sebastian.
However, he swiftly gathered his composure, realizing this must be a trap that had been laid out for him.
While the envoy gloated and unwittingly revealed his plan, Sebastian was already formulating his countermeasures.
Sebastian knew he couldn't afford to abandon his mission now.
Giving up would only make a future attempt to confront the blood gnome king all the more difficult, as the enemy would have learned from this encounter and would be better prepared next time.
Despite the blood gnome king's reputation for being brutish and not particularly wise, he was capable of learning from his experiences.
It was clear that initially, the blood gnome king hadn't counted on the support of the Demon race envoy and had wanted to defeat Sebastian on his own.