That's just due to issues in regulating gun ownership, though.
A general comparison of crimes in SK vs US: https://www.nationmaster.com/country-info/compare/South-Kore...
Interestingly, embezzlement rate seems way higher in SK.
I think the difference in the gun murder rate reflects other legal differences, such as those around carrying and storing guns more than the level of ownership. If you have to go home and unlock a safe to get a gun it gives you lots of time to cool down.