Maybe he was thinking it was a way to start a war or some ****. Attack someone who represents the US government and all. But the guy has serious mental issues though. It was told yesterday in the SK press that the guy has done this before with the shouting and ****. He went to an event from Hyundai (or sponsored by Hyundai I think?) and it had a popular boyband there called EXO (they're very huge in Korea 30,000 people attended a fan meeting of their's earlier this year from SK alone) and the guy went and was shouting the same stuff. The police investigated and saw he had mental issues. So, that explains why he thought he could slash his way to war. Guns generally aren't a thing in SK. Even the police have high restrictions for when and how etc to carry.
I'm glad he is going to be ok. I knew him back when he worked at DoD. He was always nice to me in the few interactions we had. I didn't know he had made AMBO.