Look at it this way. With Dalvik, when you open an app, the bytecode of the app is not compiled until you open the app. With ART, the bytecode is compiled when you install the app. This way, the app is practically all ready to run before you even open it for the first time. Based on the screenshot, it looks like Korean LG G2 owners will have the option to toggle between Dalvik and ART.
Those of you in the states are probably wondering when KitKat will arrive for your handset. Based on the latest info we have, KitKat should arrive for the LG G2 in the U.S. before the end of the first quarter, which ends next month.
Thanks, Anonymous Tipster!