Like most modern automatic transmissions with manual shift capability, the 9-speed has downshift rev-matching for a smoother shift and less wear and tear on the drivetrain. Although it happens in less than a second, the transmission basically shifts to neutral, revs the engine, then engages the next lower gear once the engine has accelerated to the speed that matches that gear. On the 9-speed, dog clutches are used between gears 4-5 and 7-8. Friction clutches are used between all other gears. Downshifts from 8 to 7 or 5 to 4 can feel different and/or take longer than other downshifts because extremely precise timing is required before a dog clutch can be engaged else it will grind, wear, and potentially break (like trying to shift a manual without pressing in the clutch). Shifts between other gears can occur more quickly because friction clutches don't require the timing to be as precise - if the speeds don't match, they'll just slip by design rather than clash. I doubt your dealer has a clue what a dog clutch is.