While South Korea is renowned for the Internet speed inside the country the international situation is not rosy. The only land neighbor to the North is neither friendly nor advanced so no fiber runs that way. You could run a short segment to Russia and then run a cable over there to have a short distance but it's just not economical. Instead, most of the traffic to Europe will travel over SEA-ME-WE_3 -- there's quite a lot of money to be made en route compared to a cable over the endless Russian taiga.
But that's a long and circuitous route resulting in much higher pings than a nice, straight cable with few routers en route would result in. Looking at http://verizonenterprise.com/about/network/latency we have UK to Korea around 270-300ms. http://zhiguang.me/2016/05/10/latency-between-aws-global-regions reports Frankfurt-Seoul as 266.154 avg. http://wondernetwork.com/pings reports 298ms Frankfourt-Seoul, 306ms Paris-Seoul.
Compare this to http://ipnetwork.bgtmo.ip.att.net/pws/network_delay.html the 141ms between San Francisco and Hong Kong over more than 11000 km compared to the 8540 km between Frankfurt-Seoul. In fact, if you use some of the links above you will find that the San Francisco-Europe pings are also 150ms so if you go Seoul-Hong Kong-San Francisco----New York-Europe -- you might still end up around 300ms so it's possible some traffic goes that way instead of the direct fiber all around. Certainly the 266ms doesn't, that's not possible but those close or above 300ms just might.