Huh, either knights are still commoners in this world or Hamita didn't know knights were the bottom rung of nobility with their own landed estate and a non-hereditary title. Knights are like Samurai who were also not commoners but in a different social class ranked above the plebeians. Or maybe haughty little miss noble likes to keep calling him commoner even when he's no longer one.
If this follows typical developments from the middle ages, there's a fair chance he's marrying this noble daughter and miss arrogant eccentric slave over here becomes his mistress, barring any insane plot twists. That's one way to explain why little miss noble is still here and clinging shamelessly to the "commoner" she's sponsoring.