Your suppose to use your fret hand to mute the other strings as opposed to your picking hand becuase you won't get that sweep "sound" if you don't do it like that. Even though you are getting that sound I would advise practicing it the proper way because if your just holding a chord, that will leave little room for sliding, hammer ons, pull offs and such. And when you want to start sliding or use legato in your sweeps, It'l be harder to adapt to since you were use to just holding a chord and sweeping.