The S is indeed the sports mode. The salesperson doesn't know what he's talking about. In normal drive (D) mode, you just drive like every other automatic out there. If you need some extra passing power, tap the - paddle to downshift (even though the car will do the same job if you "floor it") for a little while.

In the "S" mode, the car will stay in gear 1 when you start unless you upshift (prses the + paddle). but this mode lets you utilize the limited powerband of the car better, and gives you more control over the speed i.e. safer. I don't know if it will go all the way up to redline, I only had a brief moment test driving it in a dealer. I ended up buying a manual as they are always more fun to drive.