Tiptronics, as I learned on through this forum, have what's called a "kickdown" switch behind the pedal. If you ever press your pedal to the floor and then press with a little more force, you'll activate this switch, which will make the car go into a semi-manual sort of mode and shift down 1 or 2 gears. It will hold that gear until it either hits redline and upshifts, or will hold the gear so long as you're applying 80% or more throttle. Once you let off more than that the car will resume normal shifting. Members on here have mentioned that hitting the kickdown switch twice in quick succession is what accomplishes the 2 gear downshift. I can't speak from personal experience yet...my kickdown switch is called the clutch pedal.
I think it's a pretty neat feature and good for traffic passing without having to go into manual mode. It could be that this is what Tagonlne was doing without realizing that the car has this feature.