It doesn't have a name that I'm aware of, most people just refer to the style as a whole: "percussive guitar". Justin Sandercoe has a good lesson on it here: https://www.youtube.com/watch?v=k8_ldh4lJk8. It's not exactly the same thing but it should give you an idea of the basic principles at work so you can apply it to what Sungha and players like him do.

Also I would like to let it be known that if I'm after anyone else replying to this it's because I didn't want to stop the music playing on this page... this embedding thing has unexpected drawbacks
R.I.P. My Signature. Lost to us in the great Signature Massacre of 2014.

Quote by Master Foo
“A man who mistakes secrets for knowledge is like a man who, seeking light, hugs a candle so closely that he smothers it and burns his hand.”