Well what his guitarist is doing is muting all the unnecessary strings with his fretting hand . Then he strums everything and only the "necessary" notes will be played. This adds a nice percussion like rhythm to your playing.
Here's a very basic way to do it so you can understand what I mean.
Bare all the strings with your index finger then with your other fingers improvise around on a scale you know well. The strumming hands strums all the strings every time, naturally. So you get that "shuukkk" sound behind your melody.
Also having a good picking accuracy and muting only the strings close to the triad or the single note will help you. Having always your index rest behind is a big limitation :)