Obi-Wan and Rey
Each lightsaber is unique, designed specifically to match the creator's technique and needs. They're meant to be used by an expert in the Force, and can be dangerous in other hands. It's possible your friend is sensitive to the Force as well, but not having met him, I can't say. Did he struggle, or fight well?
The Light and the Dark refer back to two distinct philosophies as to how we should use the Force. Those of us dedicated to serving the galaxies and maintaining peace and justice are users of the light side, because we use ideals such as compassion, honesty, self-sacrifice and mercy in mind. The Dark side draws upon fear and anger for power.