So either it's incorrectly translated, or the little sister actually thinks that the empress is acting logically and Souma is action based on emotions.
This might come as a surprise to many, but the OVERWHELMING MAJORITY of people very firmly believe that any actions they take are based around sound logical reasoning. Yes, even Karens think that their actions are logical and reasonable.
This also means that anyone who acts differently must not be doing so based on logic and reason, so they have to be acting upon their own emotions.
This was the impression I got from the little sister, which might mean that it's either not actually mistranslated, or it at least makes it understandable to me of why this mistranslation would have occured.