Adana is not a city of humans, it's a city of science. You can find there Mechs, people who create or operate Mechs or Constructs, or other kinds of scientists. Sure, it wouldn't be strange to find a merchant there, but he wouldn't fit the theme.
Same can be said about other human kingdoms. A merchant can just as well be from Sword's Edge or Leonis Empire, but while he could fit there simply because there's room to all kinds of humans in such a place, he still would not fit the kingdom's main theme.
Thing is, he's a Merchant Prince - to my understanding, that means he's not prince by blood, but also not a traveling merchant. He's someone who would controls others with money, let lesser people do his work for him. I'm sure he has a lot of slaves, which would make him the best fit for Darkstone - "The Isle of the Slave Lords" - because he is a slave lord. Probably.
You're talking about the slaves. but well, they are slaves, they did not choose this lifestyle for themselves, and there's no reason to believe their enslavers share the same lifestyle.
surely you didn't have a mixup with Karakoth?
Again, on slaves. and I wouldn't be surprised if our prince here is one of the main sponsors of said experiments.