Control instinct.
That's the word that popped into Kain's head the moment Jamie finished speaking. Although he couldn't see his own expression from another's perspective, Kain was certain he hadn't shown any sign of being "dissatisfied" or anything similar.
Yet, Jamie had said he "seemed dissatisfied," which was worth noting.
Combining this with Mera's expression upon seeing the huge reward money, Kain realized that Jamie felt insecure because she couldn't control him with money. Although the relationship between the employer and the employee is equal in terms of compensation for labor, the employer always wants to control the employee in some way, because they believe they have the upper hand.
This is a common phenomenon, and it's even more understandable as Jamie is a noble, a class with a very strong desire for control.
