
Spoiler...
In the novel, Ashler and the other commander (except the commander Kin who personally recommended Mataaz) really doubt the loyalty of Mataaz but, truthfully, Mataaz is really following what the majesty had demanded him to do. Mataaz is someone who fit the best in this position because his personality is really genuine as someone who could betray his majesty for money, etc so that's why this role was given to him.
Idk if I made it clear haha.

Spoiler ahead...
I think it's the later.
We can see it as Mataaz following the order given to him by Karas thanks to his genuine character to have the ability to betray his majesty for greed or survival.
Karas is using this characteristic trait of Mataaz to proceed with his plan to deceive the King hearts (mostly Truyde) because you can't really suspect someone to deceive you if you're witnessing a genuine sense of betrayal towards his majesty for more power and wealth.
i was waiting for this ch to be translated I LOVE how he had all these tests