The situation
A server cannot tell from words or actions whether an extra portion was accepted.
English meaning: I'm fine, thank you.
Read the Japanese original
結構です。ありがとうございます。The questionWhat is the best practical response?
Read the explanation
Clues in the scene
A server cannot tell from words or actions whether an extra portion was accepted.
The scene explicitly says the waiter cannot tell acceptance from refusal.
Each choice explained
Briefly confirm whether no extra portion is wanted — Best fit
A short confirmation of whether more food is unnecessary resolves the stated ambiguity without deciding by guesswork.
Always interpret it as yes and serve more — Does not fit
No rule of automatic acceptance is given. Serving more ignores the lack of distinguishing information.
Always interpret it as no and end the conversation — Does not fit
Automatic refusal is no better supported. Ending the exchange loses the chance to confirm what was wanted.
Decide the order using birthplace alone — Does not fit
Place of origin cannot supply the missing ordering preference. The guest’s actual intention needs checking.
Same words, another scene
The guest clearly pulls the empty plate away and raises a hand in refusal before using the same words. The waiter sees the gesture and knows which food it refers to.
The additional action supports a refusal more strongly. Further clarification may still be useful if another order remains or the gesture’s target is uncertain.
I understand you do not need another serving. Is there anything else you would like?
Literal meaning
“I’m fine” is followed by “thank you.” In this scene, the server cannot tell whether the guest is accepting or declining another portion.
What these words cannot tell us
Whether the extra food is accepted or declined, and the precise object of the thanks, remain uncertain.
A question to ask in real life
Do you mean that you do not need another serving?