Dave, I could not agree more with the guy in the interview. Soft does not mean volume, that will be a function of your amp. Rather, soft touch means relaxed hands, striking the string, either with a pick, thumb or fingers with only enough energy to get a beautiful sound and no more. Play a note on your bass with with a light touch and steadily increase it, you will see there is a point at which the sound becomes unpleasant, harsh, noisy and out of tune. The studio cats, play very relaxed and that is why they sound so great. Where you play on the string gives you many sonic options too as does processing and effects.
My technique, light strings, low action, big ass amplification... I let the amp do the work, my touch provides the right amount of attack for the genre and line, light touch means I have somewhere to go when I want more intensity...dynamics!
Your bass has a sound, the wood and pickups all resonate, find where it sounds the sweetest. For me, its with a light (soft) touch and a big amp. - Great question and welcome to TB!