"What was he doing at the airport six hours before the flight?"
My previous airline was Chinese, not Korean but I suspect many of the practices are similar.
It is not uncommon to see crew in "the office" 5-6 hours before departing on a long haul flight, lurking around "building relationships". I once saw a captain in the admin office in uniform one morning "speaking to captain xxx" with a late evening departure for Europe that same day.
Oh, and its not uncommon to do a 4 hour simulator session, then have 2 hours off then PIC a long haul flight.