You're applying your own regional knowledge of English to someone else's. I'm English and I've worked as a writer and I've done copy-editing, and that 'but' has every right to be there, even if it hurts the flow of the sentence. For anyone growing up in an English speaking country we all know that a pause readily means 'but', especially if it was a longer pause.
As it's a translation of something he said, the issue here is the integrity of the translator not of the man himself. A good translator would have dropped the but, because he likely never used it when he spoke in Korean.
I've spent a lot of time in France, and even though I'm nowhere near fluent I still manage to speak the slang. By spending time in the country and amongst the people I learnt all the social norms for speaking that I never learnt in a high school class. There's a vast difference in usage between Bonsoir and Bonne nuit, the latter is literally used exclusively in the meaning "goodnight, I won't see you again today". Similarly I've seen many a confused tourist when they were greeted with Salut "bye" as a greeting.
Again from several vacations in Spain and the Spanish islands, I rarely ever heard Gracias "Thank you", they all use Graci "thanks", again despite everything I was taught of Spanish it wasn't right to how people actually speak.
There's a big difference between being fluent in a language, and being fluent in a dialect. Dialects typically teach us how to use English improperly, mainly because 90% of our interactions are informal. However almost every English speaking person would remove their dialect in the instance if they were brought in front of a world leader. I know for people receiving Knighthoods from the queen they have to instruct people on how to pronounce "ma'am" (pronounced mam) as they try to pronounce it 'properly' and in doing so pronounce it wrong, which apparently bugs the Queen herself as she's been noted for correcting people on it too.
