The Theme is the "message the author wants to give the reader".
In this case, it is "Mind your own business" and do not listen to advices that changes trivial things."
Note that:
"Huang said to the stranger, "Kindly mind your business and don't trouble over ours."
Also note that:
'His young daughter, Biyu, spoke up. "Father, you have done this well with your own ideas and choices. They have brought you success so far. You have impressed the king just by being yourself!" '
Note that in this quote, it is "own ideas and choices" which brought him "success", not other people's advice (in this case)
hope this helps