I had the pleasure , several years ago, to take the Honam HSR from Seoul to Dongdaegu , the ride was pleasant and professional , clean. The view when through Daejeon was stunning, btw. Korean country side is stellar.
Of course, South Korea has been an active investor in Turkey's infrastructure for quite some time. Both countries share quite good relations. In fact, South Korea has had historical relations with the Middle East as a whole; during the infancy years of Hyundai, Daewoo, Kia, these companies were heavily involved in infrastructure development in Saudi Arabia (Jeddah, Riyadh), which bolstered these companies' exposure to the region and confidence on their product by the locals.