Your dealer is completely wrong, and personally (watch out, here comes a rant) I can't believe that so called trained professionals, paid to know their products and sell and promote them to potential customers cant even be bothered to learn the basics and get their facts right. Unless someone's been very ill or away for a LONG period of time they should be up to speed on the car, especially pretty basic stuff like this by now.
Anyway, the sport button has NOTHING to do with the suspension, sport or otherwise.
Sports suspension is stiffer and has larger anti roll bars.
The sports button changes throttle response and steering weight/feel.
One can be ordered without the other (well, the sport button is standard on a UK S, but you know what I mean).